PROMOTIONAL FEATURE
The purpose of this study by H Lanternier and C Schwartz is to analyse the FHK prosthesis developed by Group FH ORTHO for total knee replacement
Group FH ORTHO has great experience in the design, manufacture and distribution of TKA: firstly, in the 1990s with Thémis; then in 1999 developing Academia; and in 2009 the third-generation knee prosthesis, FHK, which is the subject of this study.
General implant considerations
The femoral component and tibial tray are manufactured in CoCr for its cemented version and CoCr coated with Ti40 and HAP for the uncemented version, available in seven sizes.
The FHK is available in Cruciate retaining, Posterior Stabilized and Mobile Bearing versions [1] (see Figure 1).
Figure 1: FHK mobile bearing (left) and FHK posterior stabilised (right).
It is possible to add extension stems to the tibial tray; this is recommended in cases with poor bone quality (see Figure 2).
Figure 2: FHK mobile bearing with an additional tibial stem.
Patellar resurfacing can be done with a conventional inlay polyethylene (PE) dome implant, or with an inlay PE implant.
The tibial polyethylene is snapped on to the periphery on the tibial base in the fixed plateau version or snapped onto a central post in the mobile version.
Some original points merit further explanation:
The trochlear tracking is shifted backwards by deepening the groove. This is done by use of a trochlear chisel through the femoral cutting block. This means that patellar stress is reduced and flexion is facilitated. Furthermore, medio-lateral design has been reduced to avoid impingement onto the soft tissues.
The radius of curvature is unique (see Figure 3), which avoids instability in half flexion, and shifted slightly backwards. This improves the performance in flexion and avoids excessive pressure in extreme flexion [2].
Figure 3: FHK unique radius of curvature
The design of the femoral component directs the stresses towards the distal part of the epiphysis: the angle is sufficiently open upward (6°). The posterior surface of the trochlea is free of uncoated in order to avoid a proximal fixation and the stress–shielding where there is distal osteopenia (see Figure 4).
Figure 4: FHK half height of the anterior coating to prevent osteopenia
After the cam/spin mechanism engages, the contact point moves down the spine as flexion increases. This reduces the moment arm of the load on the spine and significantly reduces the likelihood of tibiofemoral subluxation, especially in deep flexion angles when dislocation is most likely to occur.
The tibial base on the mobile bearing implant is concave. The pressure exerted by body weight therefore causes a self-centering of the movable PE insert that relieves all the exertional force on the pivot. This also increases the contact surface area of the polyethylene base.
Implant and mechanical considerations
The polyethylene insert / tibial component interface is crucial. Obviously, dissociation of the two components would be critical, however, micro-movements within a fixed plateau are also potentially a cause for concern. The series studied below does not encounter this problem at all.
In the five-year series, no abnormal wear of the UHWPE polyethylene was seen, nor was there any evidence of geodes or loosening by macrophage reaction [3].
Mechanically, there is within this study a certain margin of safety, in that of the 62 patients in this study in the category of obese (BMI>30) there was not a single complication or revision. This contrasts with the existing literature around knee replacement in the obese patient [4].
The study found no mechanical complications related to the manufacture of the implant.
Implant and technique, surgical considerations
The FHK instrumentation is comfortable to use and is adaptable for different conditions, making it able to fit with the technique of the operating surgeon. The first or second tibial cut can be extra-or intramedullary, or combined. It is possible for the femoral referencing to be anterior or posterior. The instrumentation is sophisticated and allows for equilibrium in balance of rotations and deviations, even in complex cases [5].
The system offers a sequential analysis of these problems. We offer gauges of different thicknesses and alignments, which allow the surgeon to judge the progress of the operation. It is important to recognise and to avoid the “small surgical error” described by Pianigiani [6], which is small in its impact on kinetics but can greatly disturb balance and lead to post-operative pain.
Our experience gleaned from the production of conventional instrumentation has led to the creation of the customised cutting guide system, Only You (see Figure 5), based on CT or MRI data.
Figure 5: CT scan Only You PSI for FHK TKR
Preliminary results of a combined analysis from a prospective and retrospective, multi-centre clinical trial of 232 cases followed up for five years post-operatively.
This study is a retrospective and prospective, observational, multiple centre clinical study performed by ten surgeons in nine centres. The sample period was one year, from January to December 2011; 232 patients were operated on during this period. Of these, 16 patients died and another 44 were lost to follow-up. In total, 163 patients were reviewed at five years post-operatively.
Of the 163 cases that were reviewed at five years, with regard to pain, the main symptomatic indication for surgery, results were excellent. At five years, 58 per cent of patients reported no pain at all and 28 per cent reported episodic pain which did not necessitate analgesia. Nine cases reported pain only when climbing stairs. Three patients reported moderate pain, which occasionally required analgesia.
Conclusion
These preliminary results from a multicentric study of total knee prostheses (TKA) has a sample population which is comparable to the average population presenting for total knee arthroplasty, both in terms of age and sex distribution and for the operative indication for total knee replacement. The five-year follow-up shows an all-cause survival rate of 95.7 per cent, slightly higher than the usual 95 per cent survival rate for this type of implant. The rate of complications in relation to the implant and requiring recovery is 6.7 per cent, which is also the usual acceptable rate of revision in total knee replacement surgery. The full results will be published in the near future.
GROUP FH ORTHO would like to warmly thank all the investigators who took part in this study and their agreement to communicate the preliminary results: Pr Mainard, Pr Vastel, Dr Delannoy, Dr Furno, Dr Hummer J, Dr Hummer N, Dr Lanternier, Dr Paule, Dr Schwartz, Dr Limozin, Dr Lallement; the CEAH department of FH Orthopaedics (Centre d’ Evaluation André Hermann) and the FH LTD team for its contribution to this article.
References:
- Hilal Maradit Kremers, and others (2014) Comparative Survivorship of Different Tibial Designs in Primary Total Knee Arthroplasty J Bone Joint Surg Am. 2014;96:e121(1-7) d http://dx.doi.org/10.2106/JBJS.M.00820
- Zachary D. Post, MD, Carl Deirmengian, MD, and Jess H. Lonner, MD (2015) What’s New in Adult Reconstructive Knee Surgery J Bone Joint Surg Am. 2015;97:169-74 d http://dx.doi.org/10.2106/JBJS.N.00986
- Kathi Thiele, and others (2015) Current Failure Mechanisms After Knee Arthroplasty Have Changed: Polyethylene Wear Is Less Common in Revision Surgery J Bone Joint Surg Am. 2015;97:715-20 d http://dx.doi.org/10.2106/JBJS.M.01534
- Eric R. Wagner, and others (2016) Effect of Body Mass Index on Reoperation and Complications After Total Knee Arthroplasty J Bone Joint Surg Am. 2016;98:2052-60 d http://dx.doi.org/10.2106/JBJS.16.00093
- De Muylder J, Victor J, Cornu O, Kaminski L, (2015) Total knee arthroplasty in patients with substantial deformities using primary knee components. ). Knee Surg. Sports Traumatol. Arthrosc 23: 3653-3659
- Silvia Pianigiani, Luc Labey, Walter Pascale and Bernardo Innocenti (2016). Knee kinetics and kinematics: What are the effects of TKA malconfigurations ? Knee Surg. Sports Traumatol. Arthrosc 24:2415-2421)
