By: 8 March 2013

KWK Ho, JCF Lau and S Sadiq examine the use of the Cannulok Plus hip system in the management of complex proximal femur fractures

Complex proximal femoral fractures secondary to metastatic destruction and peri-prosthetic fractures in the elderly patient is a major management challenge. The principle treatment involves using a prosthesis that will endure the lifespan of the patient. Our objective is to review the results of a cannulated hip system in the management of these complex conditions.

A series of 19 patients aged between 50 and 102 years old (mean 78+/-13.5SD) was managed with an implantation of a fully hydroxyapatite coated and distally locked cannulated hip prostheses. 63% (12/19) were indicated due to Vancouver type B2 and B3 periprosthetic fractures of hip arthroplasty. 11% (2/19) of patients had associated metastatic bone disease, and the remaining cases were due to other pathologies associated with inadequate proximal bone stock. Primary outcome is the longevity of the implants with revision for any cause as the end point. Secondary outcome included operative complications, fracture union, length of in-patient stay and place of discharge.
Seven patients (36.8%) died from an unrelated cause at six months minimum follow-up and none of them required further revision surgery. The mean survival of the prosthesis in this group was 234 days (+/-328 SD). 12 patients still had a functional weight-bearing hip at the last review and were discharged back to their home environment. The mean survival of the prosthesis in this group was 827 days (+/-525 SD). Implant survival was 87% with revision for any reason as the end point and 100% for femoral implant revision. Five patients suffered surgical complications; three of which were hip dislocations. Of these, two required revision surgery and the other required closed manipulation. Cables and wires were used as augmentation on nine hips and distal locking screws were used on 15 hips.

In our study, 84% did not require further surgery with this prosthesis. Considering the age of this group, a high rate of mortality and morbidity was to be expected. However, none of the deceased patients required additional surgery. We found the Cannulok Plus hip system to be a valid option in the management of these conditions and to have a low chance of further surgery.

It is estimated that over 70,000 proximal hip fractures occur annually in the UK and this figure has been projected to rise to 91,500 by 2015 and 101,000 in 20201-2. This is usually due to a fragility fracture caused by a fall affecting an older person with osteoporosis or osteopenia. Currently, the average age of a hip fracture patient is 77 years and is increasing every year1.

This phenomenon, together with the increased demand for hip replacement surgery, has resulted in a rising incidence of periprosthetic hip fractures3. The management of these complex fractures in the elderly consist of medical treatment as well as an operative option using prostheses with sufficient longevity to outlast the lifespan of the patients. In order to facilitate this multi-disciplinary care approach, the surgical implant should provide sufficient stability to allow early weight bearing and mobilisation. Ease of instrumentation, low revision rate and cost-effectiveness are also significant factors to consider.

In our hospital we used the Cannulok Plus hip system (Orthodynamics Ltd, Gloucestershire, UK) which has been found useful in revision hip or complex primary arthroplasty with insufficient proximal bone stock4. It is an extensively coated femoral stem with a variable length option. It also has three distal locking screws, thereby allowing the implant to be fixed distally to improve rotational and axial stability; this facilitates load transfer to stronger intact diaphyseal bone and allows early weight-bearing. There are various modular head options ranging from 22mm to bi-polar head prostheses. However, the effectiveness of these prostheses have not been evaluated within our department.
Our objective is to review the results of the Cannulok Plus hip system in the management of complex proximal femur fractures.

All of the complex proximal femoral fractures that were treated with the Cannulok Plus hip system were reviewed. All of the cases were performed by the senior author between 2007 and 2011. Our selection criteria included those patients with a Vancouver type B2 and B3 peri-prosthetic fracture5, pathological fractures of the proximal femur secondary to metastatic bone disease, and complex fractures of the proximal femur with deficient proximal bone stock. Those with intra-capsular fractures of the hip with minimal evidence of osteoarthritis, inter-trochanteric fracture of the femur, Vancouver type A, B1 and C, abnormal femoral anatomy that would be better suited with an offset femoral stem were excluded.

19 patients (7 males and 12 females) with a mean age of 78 years (+/-13.5 SD) met our selection criteria and detailed information of these patients was retrieved from the hospital centralised computer system and patient notes. Table 1 showed the basic demographic of the study group. The following data were recorded for each patient: an assessment of the patient’s walking ability indoors and outdoors, American Society of Anesthesiologists (ASA) grade6 (1, normal healthy individual; 2, mild systemic disease that does not limit activity; 3, severe systemic disease that limits activity but is not incapacitating; 4, incapacitating systemic disease which is constantly life-threatening; 5, moribund: not expected to survive 24 hours with or without surgery; or unknown), length of hospital stay, patient’s status at discharge and the level of mobility.

The acetabular component was revised if there was evidence of loosening at the time of surgery. A modular bi-polar head articulation was used if the peri-prosthetic fracture occurs in a patient with existing hemiarthroplasty or in patients with increase risk of hip dislocation; we believed the use of modular bi-polar head would convey more hip stability and a shorter operative time.

Cables and wires were used as augmentation in nine hips to improve the stability of the construct, and the distal locking screws were used in 15 hips. Postoperatively, hip precautions were advised on all of the patients. They were allowed to sit out and fully weight-bear with the physiotherapist on the next operative day. Active mobilisation was encouraged with the help of a Zimmer frame to begin with, and followed up with crutches as soon as the pain allows. Patients may be sent to local community hospitals for further rehabilitation once medically fit for discharge.

All patients were followed up at a minimum of six months to assess clinical and radiological union of the fractures and the level of mobility was also recorded.
Our primary outcome is the longevity of the implants with revision for any cause as the end point. Secondary outcome included operative complications, length of inpatient stay, rate of fracture union and the place of discharge.

All of the data were collected and analysed using Excel spreadsheets (Microsoft Corp, Settle, WA) and SPSS 11.0 (SPSS Inc. Chicago, IL). Post-operative survival was calculated using Kaplan-Meier analysis and this was calculated both for the patient and implant survival.

In this study, 12 patients aged between 71 and 102 years old (mean 82.4 years +/- 8.8 SD) had a Vancouver grade B2 and B3 peri-prosthetic fracture. Five patients had a complex fracture of the proximal femur with deficient proximal bone stock and two patients had metastatic bone disease of the proximal femur. All patients were walking without aids prior to the fractures. Figure 1 shows those with pathological fractures were significantly younger than the others, with a mean difference of 30.2 years (+/- 7.4SD, p=0.001). The modal ASA grade of most patients was grade 3.

At the last follow-up, seven patients (37%) died from an unrelated cause; four patients died within the first six months, two patients died at one year and one patient died three years post-operation. Kaplan-Meier survival analysis shows the probability of patient survival at one year following complex proximal femoral fracture treated with the Cannulok hip prosthesis to be 53.4% (Figure 2)

The average age of the deceased group was 83.3 years old (+/-16.1 SD) and is 8.4 years older than the average age of the survivors (Figure 3). None required further revision surgery and the mean survival of the prosthesis was 234 days (+/- 328 SD). The mean survival of the prosthesis of the remaining 12 (63%) patients alive at the time of last follow-up was 827 days (+/-525 SD). All had functional weight-bearing hips at last follow-up. The average age of this group was 75 years old (+/-11.4 SD). Table 2 shows the functional outcomes and complications experienced between the two groups at follow-up. Seven patients suffered complications; two of which involved medical issues such as heart failure and urinary sepsis. Two patients suffered superficial wound infection, resolved with antibiotics. The average length of inpatient stay on our acute unit was 13.5 days (+/-10.5 SD). The majority (63%) were discharged to the rehabilitation wards and six (32%) patients were discharged directly back to their home environment.

All of the surviving hips showed radiological evidence of fracture union and no cases of subsidence of the stem were observed. Those that died within the first six months show no evidence of subsidence, however the fracture union could not be observed due to the short follow-up period.

Of the 19 patients in this study, 16 patients (84%) did not require further surgery with this prosthesis. The remaining three patients sustained their first prosthetic hip dislocations at six weeks, eight weeks, and two years post-operatively. Of these, two required open revision surgery due to recurrent dislocations and the other required manipulation under general anaesthesia. In each of the revision surgery, one was revised with a constrained hip liner, while the other with a posterior lip augmentation device (PLAD).

Kaplan-Meier survival analysis shows the probability of implant survival at one year was 86.8% with revision for any reason as the end point (Figure 4). However, the implant survival of the Cannulok femoral stem in this study period was 100%.

Our experience has shown the Cannulok Plus hip system to be a valid option to manage complex femoral pathologies with limited proximal bone stock. In view of our elderly population, often with significant medical co-morbidities, the Cannulok provides a relatively rapid recovery, with an average length of stay of less than two weeks. Of 15 patients that were alive at six months, 93% had functional weight-bearing hips and returned to their respective pre-morbid status.

In our series, 16 patients (84%) did not require further surgery with this prosthesis, and none of the patients in this study needed stem revision. Although we found two prosthetic dislocations within six months and the revision rate of 10.5% is reasonably high, we found this value consistent with many studies using long stem femoral prosthesis7-10.

None of the deceased patients suffered orthopaedic complications or needed revision surgery. We expected a high rate of mortality and morbidity because the majority of our population were elderly with significant severe medical co-morbidities (ASA grade 3). This at risk group has demonstrated a higher mortality rate of 11% to 16.5% at one year following surgical treatment, compared to a 2.9% mortality rate following primary joint arthroplasty11-12. We also agree with their conclusion that revision arthroplasty might be a better option for the treatment of Vancouver type B periprosthetic fractures compared with that of open reduction and internal fixation. Our experience with this cannulated hip system suggests the survivability of the prosthesis has outlived the lifespan of the deceased patients; and in those who are still alive, all had functional weight-bearing hips and none needed stem revision. This result is comparable to previous studies, which demonstrated that the probability of survival was 90% at five years and 79.2% at ten years, with revision or removal of the femoral implant for any reason as the end point13. However, our series were made of heterogeneous groups, an older population sample and shorter follow-up period. Therefore, a longer follow-up and review is needed to evaluate the longevity of this implant and address the long-term problems of prosthetic loosening and fracture non-union.

The prevalence of patients with hip prostheses has increased as a result of traumatic injury to the hip or hip replacement surgery3,1. One of the major complications is osteolysis of the surrounding bone and a reduction in bone stock. The changes in the bone architecture predispose it to fracture after minimal trauma. As the incidence of hip fractures is increasing with an aging population, current evidence indicates periprosthetic fractures is becoming more common, and suggests the numbers will continue to rise. Vancouver B2 and B3 periprosthetic fractures involve the femoral shaft with relatively limited bone stock, rendering it technically challenging for short stem implant. Many studies have shown plating systems in isolation to be associated with high failure rates14-20. The current consensus for treating such complex fractures involves revision of the femoral component with a long stem to bypass the fracture site by 2 cortical diameters21. We agree with existing evidence that for Vancouver B2 and B3 periprosthetic fractures a revision arthroplasty is superior to extramedullary fixation in terms of outcome22, 19, 23, 24.
Improvements in cancer treatment have also resulted in longer lifespan of the patient, when choosing a suitable prosthesis for suspected pathological fractures associated with metastatic bone disease, it is important to utilise prostheses with sufficient longevity to outlast the lifespan of the patient’s. Pathological fractures involving subtrochanteric femoral region often have structurally weak bone and unpredictable bone stock. Using conventional hip prostheses in these conditions risk future periprosthetic fractures and stem subsidence. Apart from the mechanical advantage that the Cannulock hip system provides, our experience suggests that by choosing the appropriate prosthesis, reasonable function and longevity can be expected for these patients25-32.

We recognised that there are limitations to this study. We were treating three different diagnoses with a single type of operation. We can foresee that those with metastatic bone disease will invariably have a lower survival rate than those with periprosthetic fractures. However, this only illustrates the versatility of the implant to adapt to various clinical conditions. The Cannulok Plus hip system was implemented at our centre in 2007, and even though our early results were promising, longer follow-up is yet needed to ascertain potential complications. However, amongst our elderly population, in view of prevalence of significant co-morbidity, yearly follow-up is not anticipated and all too frequently these patients become lost to the follow-up care, and outcome measurement becomes difficult. Another criticism in this study was the method of patient selection and the chance of bias from non-randomisation. However, all of the operations and the final decision for surgery were made by the senior author and this has remained unchanged for the duration of the study.

Although the Cannulok Plus hip system is showing promising results, we feel more research is yet needed as current evidence have been based on case series of small population size. We found this hip arthroplasty system to be a valid option in the management of these conditions and have a high rate of fracture healing, with immediate weight bearing, and without subsidence of the stem. It has produced predictable results, with acceptable complication and acceptable revision rate and overall good survivability in the elderly population.


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