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High-flexion Knee Designs: Is it all About the Implant?
Author: Issaq Ahmed, SpR, Department of Orthopaedic and Trauma Surgery, Queen Margaret Hospital, Dunfermline
There is an ever increasing drive to increase the range of movement after total knee arthroplasty (TKA). Some cultures all but demand it, some surgeons feel their technique enhances it, and many companies state that their design promotes it. The major goal of a primary TKA is to relieve pain whilst providing an adequate range of movement for activities of daily living. Range of movement following TKA, however, determines whether patients can manage high flexion activities such as crouching, kneeling or rising from the floor.
There are many factors other than prosthetic design, which influence flexion after TKA 1. Female gender, higher body mass index, previous surgery and other co-morbidities are associated with reduced flexion 2 while intra-operative factors such as component malposition, ‘overstuffing’ the patellofemoral joint by inserting oversized components, inadequate flexion gap balancing, failure to remove posterior osteophytes and inattention to patellofemoral tracking and thickness have been reported to have a negative effect 1. Most consistently however, the literature reports pre-operative range of movement as the best predictor of post operative range of movement 3. It has been suggested that those patients whose preoperative range of flexion was less than the mean tend to gain flexion postoperatively, whereas those with preoperative flexion greater than the mean tended to lose flexion 4. Thus there is a migration towards a mean post operatively from a broad spectrum of flexion before surgery.
The debate between whether to preserve or substitute the posterior cruciate ligament in total knee arthroplasty in order to gain flexion continues with several reviews of the literature finding insufficient evidence to recommend either 5. An implant which can achieve a deep flexion angle whilst maintaining stability has been the focus of research lately. These high-flexion prostheses include features such as reduced posterior femoral condylar radii, modifications in tibial and femoral components to accommodate extensor mechanisms with deep flexion and facilitation of physiological posterior femoral rollback. This article aims to summarise the current published studies comparing high flexion designed TKAs versus standard TKAs in order to determine whether we should be using these implants for high flexion demanding patients.
What is a high-flex knee?
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Figure 1: Design features of the NexGen LPS-Flex knee. Detailing the extra 2mm bone resection of the posterior condyles. Taken from Huang et al. The early results of high flex TKA. J Arthroplasty 2005.
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The initial concept came from Walker and Sathasivam 7 who reported that by increasing the thickness of the posterior condyle of the femoral component may overcome the edge loading and resultant increased posterior polyethylene wear and damage. The high flex design has a smaller femoral radius of curvature and thicker posterior condyle. In theory the smaller femoral radii of curvature increases the contact area between the posterior femoral condyle and the tibial insert. In addition to the thicker posterior condyle the NexGen LPS Flex (Zimmer, Warsaw, IN, USA) has a modified cam/post mechanism and an anterior cut out slope in the polyethylene insert to allow increased jump distance whilst avoiding dislocation at deep flexion angles.
Meta analysis
A recent review of the literature revealed several studies (Table 1) evaluating the effectiveness of high flexion implants in TKA 7-14. However of these nine studies only three 12, 14, 15 were prospective randomised controlled trials whilst the others were observational studies 7-11, 13. Five studies 7, 9, 10-12 reported greater flexion or range of motion with the High Flexion implant; however, the methodological rigour was questionable with inadequate blinding, flawed participant selection, short follow-up periods and functional outcomes which lacked sensitivity.
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Figure 2. Lateral views of the NexGen CR-Flex (left) and NexGen LPS-Flex (right) prostheses. Extension of the radius and thickness (2 mm) of the posterior condyle in both systems increases the articular contact area at high flexion angles and thereby increases posterior femoral translation and the range of flexion. [Pictured adapted from Functional Outcome and Range of Motion of High-Flexion Posterior Cruciate-Retaining and High-Flexion Posterior Cruciate-Substituting Total Knee Prostheses A Prospective, Randomized Study. Kim et al. JBJS Am 2009]
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The results were presented as either range of flexion or range of motion measured pre operatively and at the latest follow up. Only 2 studies 14-15 measured intraoperative flexion using the drop test. Three of the seven studies which investigated the LPS-Flex (Zimmer, Warsaw, IN, USA), the single studies involving the PFC Sigma RP-F (DePuy Orthopaedics, Inc., Warsaw, IN, USA) and the Genesis II High-flex PS (Smith & Nephew, Memphis, TN, USA) showed significant gains in their respective trials.
Functional outcome measures were reported in eight studies, the most common being the Knee Society Score (KSS) in five studies 7, 9, 10, 12, 14 and the Hospital for Special Surgery (HSS) Knee Score in two studies 8,11 while one study used both 15. Nutton et al. 14 also evaluated maximal functional knee flexion measured by electrogoniometry during various tasks. None of these studies showed any significant differences between the groups with these scores (p>0.05).
Table 1 – Summary of the current published literature.
|
Implant
used |
Study
design |
n
(patients) |
Follow up (years) |
| Huang (2005) 7 |
LPS |
Case controlled |
|
|
|
LPS-F |
(retrospective) |
28(28) |
2 |
| Seon (2005) 8 |
LPS |
Case Controlled |
50(50) |
2 |
|
LPS-F |
|
|
|
| Gupta (2006) 9 |
PFC Sigma |
Case controlled |
50(45) |
1 |
|
PFC Sigma RP-F |
|
50(45) |
|
| Laskin (2007) 10 |
Genesis II PS |
Case controlled |
40(40) |
2 |
|
Genesis II High flex |
|
40(40) |
|
| Bin (2007) 11 |
LPS |
Case Controlled |
97(69) |
1 |
|
LPS-F |
|
96(72) |
|
| Weeden (2007) 12 |
LPS |
RCT |
25(25) |
1 |
|
LPS-F |
|
25(25) |
|
| Ng (2008) 13 |
LPS |
Case Controlled |
35(35) |
2 |
|
LPS-F |
bilateral |
35(35) |
|
| Nutton (2008) 14 |
LPS |
RCT |
28(28) |
1 |
|
LPS-F |
(Double blinded) |
28(28) |
|
| Kim (2009) 15 |
LPS |
RCT, bilateral |
250(125) |
2 |
|
LPS-F |
|
250(125) |
|
n - number of implants (number of patients).
RCT – randomised controlled trial.
By far the largest Level 1 prospective double blind randomised controlled study by Kim et al 15 investigated whether there was an advantage to using either a posterior cruciate-retaining or posterior cruciate-substituting design. Two hundred and fifty patients received a high-flexion posterior cruciate retaining prosthesis in one knee and high-flexion posterior stabilised total knee prosthesis in the contralateral knee. Patients were assessed clinically by determining range of motion, both radiographically and functionally, with use of the knee rating systems of the Knee Society and the Hospital for Special Surgery. In addition, each patient completed the Western Ontario and McMaster Universities Osteoarthritis (WOMAC) questionnaire. The authors found no difference in the ROM or in the clinical and radiographic results between knees that received a high-flexion cruciate-retaining or stabilized prosthesis.
The major strength of this study was that the patients acted as their own controls. Furthermore, patients were assessed clinically, radiographically, and by functional outcome by an independent observer. In addition all of the operations were carried out by one surgeon. Weaknesses of the study were that this was an Asian population of predominantly female patients and that the findings may not necessarily be transferable to other populations. In addition, when bilateral procedures are performed, it may be difficult to separate the functional outcome for one of the individual knees.
There are concerns that efforts to increase maximum flexion may negatively impact implant survival. Ranawat noted that shortening the posterior radius by removing more bone would result in instability and increased patellar and tibial stresses [16]. Other authors have shown increasing contact stresses with increasing flexion and translation of the femoro-tibial contact point, leading to potentially greater wear and earlier failure of polyethylene inserts [17, 18]. This is particularly concerning with the growing proportion of younger patients with higher functional demands receiving TKA.
Conclusion
This article set out to answer the question as to whether we should be using High flexion implants in patients who already have good ROM prior to their knee replacement or in the ‘High flexion user’. However, the current evidence for the improved clinical benefit of using these implants in TKA over traditional implants is conflicting. More importantly none of the studies reviewed investigated the effect of these implants in patients who have good ROM (>120 degrees) prior to their surgery. Further long term studies focusing particularly on these high flexion patients are required to determine whether these patients truly benefit from these implants. The hypothesis being that those patients with good flexion prior to surgery should go on to achieve the same flexion with or without a high flexion designed implant.
There may be no doubt that theoretically High Flex design total knee replacements should help gain or increase range of motion after TKA. Methodological limitations, inconsistencies in high flexion TKA published research along with uncertain long term survivorship lead me to conclude that there is currently no established benefit in post operative knee ROM or physical function when using a High flexion implant.
References
- Dennis DA, Komistek RD, Scuderi GR, Zingde S (2007) Factors affecting flexion after total knee arthroplasty. Clin Orthop Relat Res 464:53–60
- Fisher DA, Dierckman B, Watts MR, Davis K (2007) Looks good but feels bad: factors that contribute to poor results after total knee arthroplasty. J Arthroplasty 22(6 Suppl 2):39–42
- Ritter MA, Harty LD, Davis KE et al (2003) Predicting range of motion after total knee arthroplasty. Clustering, log-linear regression, and regression tree analysis. J Bone Joint Surg Am 85:1278–1285
- Scott RD, Volatile TB. Twelve years’ experience with posterior cruciate-retaining total knee arthroplasty. Clin Orthop Relat Res. 1986; 205:100-7.
- Argenson JN, Scuderi GR, Komistek RD et al (2005) In vivo kinematic evaluation and design considerations related to high flexion in total knee arthroplasty. J Biomech 38:277–284
- Walker PS. Sathasivam S. Design forms of total knee replacement. IMechE 2000 Vik 214(H): 101-119
- Huang HT, Su JY, Wang GJ. The early results of high-flex total knee arthroplasty: a minimum of 2 years of follow-up. J Arthroplasty 2005. 20:674–679
- Seon JK, Song EK, Lee JY (2005) Comparison of range of motion of high-flexion prosthesis and mobile-bearing prosthesis in total knee arthroplasty. Orthopedics 28(10 Suppl):s1247–s1250
- Gupta SK, Ranawat AS, Shah Vet al (2006) The P.F.C. sigma RPF TKA designed for improved performance: A matched-pair study. Orthopedics 29(9 Suppl):S49–S52
- Laskin RS. The effect of a high-flex implant on postoperative flexion after primary total knee arthroplasty. Orthopedics 2007: 30(8 Suppl): 86–88
- Bin SI, Nam TS. Early results of high-flex total knee arthroplasty: comparison study at 1 year after surgery. Knee Surg Sports Traumatol Arthrosc 2007: 15:350–355
- Weeden SH, Schmidt R. A randomized, prospective study of primary total knee components designed for increased flexion. J Arthroplasty 2007: 22:349–352
- Ng FY, Wong HL, Yau WP et al Comparison of range of motion after standard and high-flexion posterior stabilised total knee replacement. Int Orthop 2008: 32:795–798
- Nutton RW, van der Linden ML, Rowe PJ et al (2008) A prospective randomised double-blind study of functional outcome and range of flexion following total knee replacement with the NexGen standard and high flexion components. J Bone Joint Surg Br 90:37–42
- Kim YH, Choi Y, Kwon O-R and Kim JS. High-Flexion Posterior Cruciate-Substituting Total Knee Prostheses. A Prospective, Randomized Study. J Bone Joint Surg Am. 2009; 91:753-60
- Ranawat CS (2003) Design may be counterproductive for optimizing flexion after TKR. Clin Orthop Relat Res 416:174–176
- Han HS, Kang SB, Yoon KS (2007) High incidence of loosening of the femoral component in legacy posterior stabilised-flex total knee replacement. J Bone Joint Surg Br 89:1457–1461
- Akagi M, Nakamura T, Matsusue Y et al (2000) The Bisurface total knee replacement: a unique design for flexion. Four-to-nine year follow-up study. J Bone Joint Surg Am 82:1626–1633
Alternatives to Allogeneic Blood – A Pilot Study
Author: Jonathan Trattles, Transfusion Practitioner, Sunderland Royal Hospital
The blood supply in the UK is one of the safest anywhere but it remains an expensive resource. The use of allogeneic transfusion has in recent years been re-evaluated due to concerns raised over the risks of transfusion transmitted infections, immunologic reactions and human error catastrophes. Recent attention has focused on the transmission of variant Creutzfeldt-Jakob Disease (vCJD). This is a rare and fatal human neurodegenerative condition which is transmitted by a prion from meat infected with BSE.
 In 2004 a report published in The Lancet demonstrated that vCJD can be transmitted by blood transfusions1 and at the time of writing there have been four known such cases. This led the UK to exclude donors who have, or think they may have, received a blood transfusion since 1980 from donating blood. This step was implemented by all four of the UK Blood Services on 2nd August 2004.2
The increased cost of blood products, combined with the potential risk of transmission of disease and donor shortages, has been the driving force in medical circles to conserve blood supplies through the judicious use of allogeneic blood and to adopt alternatives to minimize patient exposure to the risks of such transfusions.
The use of red cell salvage techniques to complement a blood conservation program is accepted practice. This form of autologous blood transfusion involves the collection and re-infusion of the patient’s own blood. Post operative cell salvage is a subtype of autologous blood transfusion. In this technique the blood from the operative site is collected post operatively through conventional drains and subsequently re-infused back to the same patient. This form of autologous blood transfusion is especially useful in joint replacement surgery such as total knee replacements and total hip replacements.
Total knee replacement (TKR) surgery can result in substantial blood loss.3 It is estimated that 50% of the true total loss occurs during the post-operative period which suggests salvage and re-infusion of shed blood presents an effective means of reducing the requirement for allogeneic blood.
A pilot study was conducted in a large district general hospital in the North East of England, that issues approximately 11,500 units of blood per annum. The hospital has an established and proactive transfusion team and has already successfully introduced intraoperative red cell salvage. It was decided to pilot the use of CellTrans™ (Summit Medical) autologous blood transfusion system.
Prior to the introduction of autologous blood transfusion systems, a preliminary study was undertaken to develop and validate criteria in order to target the use of the drains to patients most likely to benefit from their use. A study of 200 patients admitted for knee arthroplasty identified a transfusion rate of 26%. A total of 108 units of bank blood were used in this cohort, with a mean of 2 units per patient transfused. This equated to approximately £15,800 for the units of blood used. It was discovered the mean procedural drop in Hb was 4.8 g/dl (range 2.3 – 8.8 g/dl). This allowed the formulation of inclusion criteria for patients most likely to benefit from autologous drains.
Patients considered for inclusion in the pilot must
- be under the care of a Consultant Orthopaedic Surgeon with experience in blood conservation techniques and familiar with the CellTrans™ drain
- be undergoing bilateral or revision knee surgery
- be undergoing primary knee replacement where the pre-op Hb <50 g/l above the patient’s individual transfusion trigger established by the anaesthetist
- be assessed for contraindication and consent gained by an anaesthetist who would decide on patient suitability.
 In order to validate these criteria, the criteria were applied to the pre-study cohort. It was established that all of the transfused patients met the criteria. Of those meeting the criteria, 13% would have avoided transfusion. None of the patients who would have been excluded from receiving drains were transfused. Of the 200 patients studied, 35% met the criteria.
Prior to commencing the study, an operating policy was developed and ratified along with a data collection tool. Staff competencies were developed and ratified and education sessions were delivered by the manufacturer to 100 staff. A number of key trainers were identified and given appropriate training.
During the pilot period, 50 patients met the inclusion criteria and received autologous drains. Of this group, 33 underwent unilateral knee arthroplasty, 13 bilateral and 4 revision procedures. The mean volume of blood re-infused was 600 mls and the average procedural drop was 2.9 g/dl.
Evaluation of the pilot demonstrated a reduction in the overall transfusion rate from 26% to 3% with only 4 of the 50 patients requiring bank blood. This reduction was more dramatic in those undergoing bilateral and revision procedures where blood use was reduced from >95% to 12%. There were no adverse events noted in the pilot period, and staff were instructed not to reinfuse blood if there were any uncertainties regarding the procedure.
The cost of the blood used during the pilot combined with the additional cost of the drains was £6230. This represented a cost saving of £7500 when compared with the expected use of blood within this group.
The conclusions from the pilot were that:
- Post-operative autologous transfusion is a safe and efficient way to reduce patient’s exposure to donor blood
- The use of drains directed at a target population is an appropriate strategy
The key factor in the successful introduction of post operative blood salvage is continued staff training
References
- Peden AH, Head MW, Ritchie DL, Bell JE, Ironside JW (2004). “Preclinical vCJD after blood transfusion in a PRNP codon 129 heterozygous patient”. Lancet. 2004, 364 (9433): 527-529
- National Blood Service http://www.blood.co.uk/pages/b10faq.html
- Lotke PA, Faralli VJ, Orenstein EM and Ecker ML. Blood loss after total knee replacement. Effects of tourniquet release and continuous passive motion. JBJS.1991:73,(7); 1037-1040.
Computer Navigation in Total Knee Arthroplasty
Authors: Ayaz Lakdawala MRCS, MBBS - SpR - Trauma & Orthopaedics, Royal Orthopaedic Hospital, Birmingham
Nick Rouholamin MRCS - SpR - Trauma & Orthopaedics, Russells Hall Hospital, Dudley
Nadim Aslam FRCS (Orth) - Consultant Orthopaedic Surgeon - Worcestershire Royal Hospital, Worcester
Introduction
Component alignment and ligament balancing are critical factors in achieving a successful functional outcome following TKA1. Malalignment is an important cause of early failure. This can cause pain, instability, reduced range of movement, excessive polyethylene wear, and subsequent implant loosening. Conventional instrumentation uses anatomical bony landmarks. Reference errors with these landmarks can occur because these are either invisible (e.g., femoral head), virtual (e.g., mechanical axis) and difficult in the presence of associated deformities. Computer-assisted surgery (CAS) technology allows intra-operative quantitative measurements of axes. This information assists the surgeon in achieving component alignment and improved balancing of the knee, thereby avoiding the “outliers” in the alignment of the mechanical axis.
CAS: The Technology
Overall there are two mainstream technologies in current use: image based and imageless CAS. The former usually uses fluoroscopic assistance and has the ability to create a spatial link between the image and anatomical landmarks, the defined virtual points, planes, and axes. This enables the surgeon to visualise the fluoroscopic image of the implants intra-operatively and has control of every step in the procedure. Thus, with an image-based system, the surgeon can define the landmarks kinematically as well as visually. However, this has certain drawbacks. The fluoroscope is bulky, needs larger operating field & there is a potential radiation hazard. The imageless CAS is cheaper, less bulky, and easier to use.
 In CT-based systems, scans are obtained pre-op and, intra-operatively the surgical field is registered and defined using either a surface-based or point-based system. Surface-based registration can provide a virtual 3D image and also provides assessment of bone density. This technique uses more radiation and can be costly.
The alternative is an image-free navigation. In this technique, the key anatomical references points (centre of the hip and ankle) are digitised by the surgeon. Accuracy is user dependent & complete 3D images cannot be obtained.
‘Bone Morphing’ is a newer technique and it provides complete 3D images. The computer computes the points digitised on the articular surfaces of the tibia and/or femur. Here the registration is done intra-operatively between the anatomical data and the statistical model. It cannot provide information on bone-density.
Virtual fluoroscopy is a system which does not require a registration procedure. The principle is to navigate on calibrated fluoroscopy images. After two to three images are acquired, the C-arm is removed. The images are 2-dimensional and expose the staff to radiation.
For the femoral component, the CAS technology provides the surgeon with precise information on flexion/extension and varus/valgus. For the tibial component, it provides more precise information regarding the orientation of tibial slope and varus/valgus positioning. This can assist in achieving more precise alignment and flexion/extension balancing of the knee.
Computer Assisted TKR Vs Conventional TKR
Different authors have published their experiences with these systems. A recent meta-analysis has shown more accurate AP & lateral alignment of the tibial and femoral components with fewer outliers outside the range of 3° varus or valgus 3. Some studies have shown no clinically significant difference between CAS & conventional TKR 4-6.
Sikorski 7 highlighted the limitations of the CAS to help identify rotational malalignment. Correct rotational alignment of a TKA is important to achieve optimal patellar tracking and implant longevity. In a randomised study, Lutzner et al 8; did not find any notable difference between CAS and conventional TKR techniques with regards to rotational alignment of the femoral or tibial components.
There is a steep learning curve, not only for the surgeon but also for the nursing staff. The operating time with CAS is longer than conventional technique because of the set-up and data acquisition 2. Most studies show not difference in blood-loss between the CAS and conventional technique. Functional results are also similar at 2 yrs 9. At present there is no long-term follow-up available on TKR using CAS technology.
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| BrainLAB’s knee essential software |
CAS in Revision TKR
Common cause of revision TKR is aseptic loosening of the tibial components and instability due to inadequate balancing of the flexion/ extension gaps. In revision surgery the challenge is restoring the joint line and stability. This can be complicated by associated bone loss and difficulty in identifying relevant bony landmarks. CAS can help aid alignment and restore the joint line, however further information on CAS in revision TKR is required in the literature.
Future Challenges
Different CAS imaging modalities are emerging. Recently bone morphing has been introduced, allowing visualisation of a 3D surface of the bone intra-operatively. Accuracy of these new technologies needs to be clinically validated and devices need to be regulated. What is needed is a CAS system that does not require pre-operative imaging, allows 3D reconstruction, uses percutaneous techniques of registration and is easy to use. It would be desirable to have a system that also facilitates minimally invasive TKR.
Summary
CAS is still evolving and new technologies are emerging. It has a definite advantage in achieving precise component alignment but there is a learning curve. It can be particularly useful in planning TKR in presence of deformities around the knee.
It remains to be seen whether long-term results of TKR can be improved using CAS technology. It is possible that in the future, CAS will be more widely used especially as the new generation of trainees will most likely “grow up” with this concept and practice.
References
- Insall JN. Surgery of the knee. 2nd Edition . New York: Churchill Livingstone, 1993.
- Victor, J. Computer assisted surgery: Coronal and sagittal alignment. In Total Knee Arthroplasty: A Guide to Get Better Performance, edited by J. Bellemans, M. D.Ries, J.Victor, Springer, New York.
- Bauwens K, Matthes G, Wich M, et al. Navigated total knee replacement: a meta-analysis. J Bone Joint Surg [Am] 2007; 89-A:261-9
- Ensini A, Catani F, Leardini A, et al. Alignments and clinical results in conventional and navigated total knee arthroplasty. Clin Orthop 2007; 457:156-62.
- Stulberg SD, Yaffe MA, Koo SS. Computer- assisted surgery versus manual total knee arthroplasty: a case controlled study. J Bone Joint Surg [Am] 2006; 88-A (Suppl 4): 47-54.
- Kim YH, Kim JS, Yoon SH. Alignment and orientation of the components in total knee replacements with and without navigation support: a prospective, randomised study. J Bone Joint Surg [Br] 2007; 89-B:471-6.
- Sikorski, J. M. Computer assisted surgery and rotational alignment of total knee arthroplasty. In Total Knee Arthroplasty: A Guide to Get Better Performance, chap. 40, edited by J. Bellemans, M. D. Ries, J. Victor, Springer, New York, 2005.
- Lutzner J, Krummenauer F, Wolf C, Gunther K.P., Kirshner S. Computer-assisted and conventional total knee replacement. A comparative, prospective, randomised study with radiological and CT evaluation. J Bone Joint Surg [Br] 2008;90-B:1039-44.
- Spencer JM, Chauhan SK, Sloan K, Taylor A, Beaver RJ. Computer- navigation versus conventional total knee replacement: no difference in the functional results at two years. J Bone Joint Surg [Br] 2007; 89-B: 477-80.
The Biomechanical Evidence for Valgus Knee Bracing in Medial Compartment Osteoarthritis
Author: Jim Richards, Professor of Biomechanics, School of Public Health & Clinical Sciences, University of Central Lancashire
Introduction
The use of knee orthoses to correct and to support moments about joints is one of the most common uses of direct orthotic management. In the case of knee valgus braces the aims are to unload the painful compartment through bending moments applied proximally and distally to the knee joint and to reduce the varus deformity (Pollo, 1998). Several studies have been conducted into the use of valgus knee braces for medial compartment osteoarthritis and have reported that patients experience significant pain relief and an improvement in physical function (Hewett et al, 1998; Kirkley et al, 1999; Lindenfeld et al, 1997; Matsumo et al, 1997; Richards et al 2005) and also a reduction in medial compartment load (Pollo et al, 2002; Jones et al, 2006).
But how can a valgus brace reduce the load on the medial compartment of the knee? The answer is that this is a very hard thing to measure directly; however, measures that give an indirect indication of the loading on the medial compartment are a reduction in the knee adduction moments and the varus angle of the knee.
It is widely known that knee osteoarthritis is more prevalent in the medial compartment of the knee joint than the lateral compartment and it has been estimated that during normal gait approximately 60–80% of the load across the knee joint is transmitted to the medial compartment (Prodromos et al, 1985).
During walking, individuals have an almost continuous large, external varus moment about their knees throughout stance phase, with the exception of a small valgus moment at initial contact (Johnson et al, 1980, Matsumo et al, 1997). It has been suggested that this varus or adduction moment and the increased loads are a causation factor for the incidence of medial compartment osteoarthritis (Goh et al, 1993). These increasing loads have a degenerative effect on the cartilage in the medial compartment with a narrowing in the joint space between the medial femur and medial tibial plateau. This causes a moment arm increased over that of the unaffected side in a control population (Wang et al, 1990). Increasing disability will therefore arise from the increased moment arm with pain and functional impairment being the principal complaints of knee osteoarthritis sufferers (Kim et al, 2004), ultimately leading to a reduced quality of life.
Treatment options available to the sufferer are aimed at minimizing these forces at the medial compartment of the knee (Pollo, 1998). Surgical options such as high tibial osteotomy (HTO) and unicompartmental arthroplasty attempt to unload the medial compartment by realigning the tibia, and decrease the loading at the medial compartment by transferring the load to the less affected lateral compartment (Maly et al, 2002; Noyes et al, 1992).
However, these types of surgery may not be appropriate for many individuals, therefore conservative treatment modalities have been introduced in an attempt to reduce this excessive compartmental loading without the need for surgical intervention. One form of conservative treatment for medial compartment osteoarthritis of the knee is valgus bracing. Valgus braces often claim more than just the ability to support and often claim to offload the painful compartment, correct the varus alignment of the knee and improve quality of life. Various studies have investigated the biomechanical effects and the pain reduction using such devices.
Biomechanical Changes seen with Valgus Bracing
Varus knee angle
The effect of valgus bracing on knee varus has been a point of debate for some time; however, recent research (Pollo et al, 2002; Jones et al, 2006) has shown that bracing can have a direct effect on the knee angulation in the coronal plane. The data below show the immediate effect of an individual with medial compartment knee OA walking with and without a valgus brace. The brace fitted in this instance was an OA Adjuster (DJO), which allows the clinician to dial in a ‘correction’. In this case the brace was adjusted until contact was made with the lateral aspect of the knee joint, and then a further 5° was dialed in.
This was to first take up the slack in the brace, and then to try to correct by a further 5°. The greatest effect in the varus angle is during loading response from 0 to 20% of the gait cycle (Figure 1). At approximately 10% of the gait cycle, the point of greatest loading, the difference between the braced and unbraced conditions was 4°, indicating that actual correction is in a similar order to the dial in correction, which in turn will reduce the moment arm of the ground reaction force in the coronal plane.
 |
| Figure 1: Varus angle from 0 to 50% of the gait cycle |
Knee adduction moments
Kim et al (2004) looked at the adduction moment in individuals with and without medial compartment knee osteoarthritis. They found a significant difference in the adduction moment between the osteoarthritis group and an age and gender matched normal group; the osteoarthritis group having on average a 50% increase in their adduction moments. Kim also found a correlation between knee adduction moments with the WOMAC Score. This supports the comments by Goh et al (1993), who suggested that the adduction moment and the increased loads are a causation factor for the incidence of medial compartment osteoarthritis. The reduction in the varus deformity during loading, should in turn lead to a reduction in the adduction moment about the knee joint. Figure 2 shows that this is indeed the case, with the braced condition reducing the adduction moment by 13%.
 |
| Figure 2: Adduction moments normalized to body mass |
Ground reaction forces
Ground reaction forces give useful information about the loading and propulsion during walking. For both the vertical and anterior posterior forces, increases in the loading and propulsive forces are seen (Figure 3) when wearing the valgus brace. But isn’t an increase in force bad? The ground reaction forces do not tell us much about the loading patterns within the knee; however, they are useful in determining how well an individual can load and push off during walking, the larger vertical loading and propulsive forces indicating an improved weight acceptance and propulsion.
 |
| Figure 3: Vertical and anterior posterior forces with and without bracing normalized to body weight |
Summary and Conclusion
Overall, these findings show that valgus bracing can give a degree of correction to the varus deformity of the medial compartment osteoarthritic knee and a reduced adduction moment, which gives the subject substantial functional improvements during gait. Although this appears to be very clear evidence for the mechanical effect of valgus bracing, further research is needed on the effect of different designs and different amounts of correction. Can we, for instance, get the same amount of correction using a smaller brace, and what is the limit of correction we can achieve either by building the correction into the brace or by dialing the correction into the brace?
References
- Goh JC, Bose K, Khoo BC. Gait analysis study on patients with varus osteoarthrosis of the knee. Clinical Orthopaedics and Related Research 1993;(294):223–231.
- Hewett TE, Noyes FR, Barber-Westin SD, Heckmann T. Decrease in knee joint pain and increase in function in patients with medial compartment arthrosis: a prospective analysis of valgus bracing. Orthopedics 1998;21:131–138.
- Johnson F, Leitl S, Waugh W. The distribution of load across the knee. A comparison of static and dynamic measurements. British Journal of Bone and Joint Surgery 1980;62(3):346–349.
- Jones RK, Nester CJ, Kim WY, Tyson S, Laxton P, Jari S, Johnson D, Richards JD. Direct and indirect orthotic management of medial compartment osteoarthritis of the knee, ESMAC & GCMAS meeting, Amsterdam, 25–30 September, 2006.
- Kim WY, Richards JD, Jones RK, Hegab A. Single limb stance adduction moment in medial compartment osteoarthritis of the knee. The Knee 2004;11:225–231.
- Kirkley A, Webster-Bogaert S, Litchfi eld R, Amendola A, MacDonald S, McCalden R, Fowler P. The effect of bracing on varus gonarthrosis. American Journal of Bone and Joint Surgery 1999;81–A:539–548.
- Lindenfeld TN, Hewett TE, Andriacchi TP. Joint loading with valgus bracing in patients with varus gonarthrosis. Clinical Orthopaedics 1997; 344:290–297.
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Sandvik – From Metallurgy to Medical
Introduction
In May 2007, global engineering group Sandvik extended its presence in the fast-moving medical sector by acquiring specialist orthopaedic manufacturing expertise.
Since then, Sandvik has made further strategic acquisitions. Each one has enhanced its capability in the sector. At the same time, Sandvik is underpinning the new organization with the combination of its metallurgical expertise, long-standing commitment to research and development (R&D) and partnership approach.
Consequently, Sandvik is now truly seen as ‘one to watch’.
Simon Grant, Vice President at Sandvik, explained: “Sandvik was founded by Göran Fredrik Göransson in 1862. His goal was to provide high quality, highly-engineered products and added value through investment in R&D and genuine partnerships. This approach reflects that of our customers and, combined with Sandvik’s specific capabilities, is fundamental to success in the medical marketplace.
“The emphasis in the sector on product and process development and innovation means our customers also need strong long term partners. Sandvik is a global business, employing over 47,000 people across 130 countries. Our track record is that of well-managed, profitable growth so our customers can have real confidence in the stability of the company.”
 Metallurgical expertise
At the centre of Sandvik’s operations is its extensive metallurgical expertise – a key capability in the medical sector, where a thorough understanding of biocompatibility and the potential offered by a range of alloys can lead to real innovation in the marketplace.
Simon explained: “We supply a range of stainless steel, non-ferrous alloys and special alloys to exacting specifications for a variety of applications. We can also manufacture metallic materials in a variety of forms including strip, bar, flats, wire, profile, tube and fine metal powder. This in-house capability means we can control quality and cut time-to-market for our customers by reducing third-party supply-chain delays.
“Our ultimate goal is to provide a complete, end-to-end solution that will enable us to take full responsibility for quality and tracking issues, right from melt through to finished component.”
The role of R&D
Sandvik’s metallurgical expertise has been built on the company’s original foundation stone of its commitment to R&D.
Tom Ericksson, R&D Manager at Sandvik, explained: “In addition to Northern Europe’s largest R&D facilities for the development of advanced metallic and ceramic materials, we have also recently created a bespoke R&D team, based in Sandviken, to focus on the medical product marketplace.
 “We have significant expertise in medical surface modifications and medical alloys, mainly Titanium and Cobalt Chromium Molybdenum, and are also involved in a number of exciting projects that will deliver real value for our customers over the next few years.
“The key is that, with 3% of invoiced sales being reinvested into R&D throughout the Sandvik Group, we can take a longer-term view of our research programs, enabling us to become genuine scientific partners to our customers.”
Sandvik today
Simon Grant concluded: “While the medical marketplace is fundamentally different to all Sandvik’s other markets, we believe it provides a strong fit with our core competencies and that we can bring a unique offer to the market.
“The medical sector is growing rapidly, with longer life expectancy changing the demographics of the Western world. Add to this the impact of obesity and an expectation among patients that they will continue with an active lifestyle post surgery, and it is clear that medical device and instrumentation companies must continually evolve and quickly bring new and effective technologies to market.
“By combining our metallurgical expertise, commitment to R&D and medical sector capability we are doing just this, helping our customers improve speed to market, productivity, and scientific and environmental performance. At the same time we are becoming a true supply-chain integrator.
“By working with Sandvik, customers increase profitability and market share; in turn, we will achieve our own commercial goals. A win-win situation for all concerned!”
www.sandvik.com/medical
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