Aims

In the native hip, the hip capsular ligaments tighten at the limits of range of hip motion and may provide a passive stabilizing force to protect the hip against edge loading. In this study we quantified the stabilizing force vectors generated by capsular ligaments at extreme range of motion (ROM), and examined their ability to prevent edge loading.

Introduction:

There has been widespread concern regarding the adverse tissue reactions after metal-on-metal (MoM) total hip replacements (THR). Concerns have also been expressed with mechanical wear from micromotion and fretting corrosion at the head/stem taper junction in total hip replacements. In order to understand the interface mechanism a study was undertaken in order to investigate the effect of surface finish and contact area associated with modular tapers in total hip replacements with a single combination of materials of modular tapers.

INTRODUCTION

A recent PRCT failed to demonstrate superiority of HRA over THA at low speeds. Having seen HRA walk much faster, we wondered if faster walking speed might reveal larger differences.

We therefore asked two simple questions:

Does fast or uphill walking have an effect on the observed difference in gait between limbs implanted with one HRA and one THA?

If there is a difference in gait between HRA and THA implanted legs, which is more normal?

Introduction: One of the most important factors affecting the outcome of revision THR of the femoral stem is the variability of femoral endosteal geometry after removal of the in-situ stem. A custom made implant would greatly reduce the inventory of the ‘Off the shelf” (OTS) components. This study presents the medium to long-term results of a cohort of patients with this revision prosthesis.

Methods: During the period November 1991 to November 1998, 158 patients were implanted with a computer-assisted design and computer-assisted manufactured (CAD-CAM) revision prostheses (Stanmore Implants Worldwide, Biomedical Engineering Unit, RNOH) by the senior author (SMA). There were 97 males and 61 females. The average age was 63.1 years (34.6 – 85.9). The indications for revision surgery were aseptic loosening (135 cases, 85.4 %), peri-prosthetic fractures (6 cases, 3.8 %), infection (12 cases, 7.6%) and liner wear (3 cases, 1.9%).

Results: At 10 years all patients reported relief of pre-operative pain and the average hip flexion was 95o (90 o –110o). Oxford, Harris and WOMAC hip scores in the pre-operative and post-operative period were 41.1, 44.2 and 52.4 respectively and 18.2, 89.3 and 12.3 respectively (p< 0.0001, p< 0.0001, p< 0.0001).

There were 6 complications (3.8%) in this series; a periprosthetic fracture of the femoral diaphysis (1), posterior dislocation (2), failure secondary to aseptic loosening of the implant (1) and deep vein thromboses (2)

Discussion: These ten year results are encouraging and suggest that there is a role for the use of custom implants in revision THR, particularly where the anatomical variance of the proximal femur makes the use of OTS implants unsuitable.

Introduction: The conversion of the fused hip to a total hip replacement poses a challenging reconstructive problem. The technical pitfalls depend on the aetiology of the arthrodesis, the surgical technique used and the available bone stock. Indications include painful pseudo arthrosis, disabling back or ipsilateral knee pain and malposition of the arthrodesed hip. There are often difficulties restoring appropriate biomechanics and providing a functionally useful outcome. We present a short series where a custom CAD/CAM femoral prosthesis was used to accommodate the anatomical problems caused by previous spontaneous and operative arthrodesis.

Patients and Method: 5 patients (4 female, 1 male) with primary diagnoses of septic arthritis, TB, trauma and DDH were reviewed. The average age at the time of conversion was 43.6 years (Range 20–62 years). The patients were reviewed with a mean follow up of 82 months (Range 24–110 months). All the patients were evaluated by an independent observer radiologically and clinically using Harris, WOMAC and Oxford hip scores.

Results: The patients improved from preoperative HHS 55 (Range 39–73), Oxford 40 (Range 37–46) and WOMAC 80 (Range 65–92) to postoperative HHS 73 (Range 44–94), Oxford 26 (Range 17–42) and WOMAC 45 (Range 24–79). These results compare poorly to a large series of age and sex matched cases undergoing primary and revision hip arthroplasty. Nevertheless, 4 patients were extremely satisfied with the results of their operation. 1 patient showed no improvement in his scores although he reports that his spinal symptoms are better. His operation was complicated by non-union of the greater trochanter.

Conclusion: Most series report poor results after the conversion of arthrodeses to total hip replacements. The commonest problems include instability, sepsis, fractures, limited mobility of the hip replacement and poor function. Careful planning is required to accommodate the atypical anatomy. The use of CAD/CAM femoral stems in the conversion of the arthrodesed hip has allowed preservation of valuable bone stock in anatomically abnormal femora whilst optimising biomechanics and improving function.

An observation was made in our unit that sciatic nerve injury following total hip arthroplasty seemed to be more common in women. This observation has been mentioned in the literature, but no anatomical explanation has been postulated. We aimed to confirm this and suggest an anatomical explanation.

Members of the British Hip Society were approached by means of a postal questionnaire regarding the sex incidence of sciatic nerve injury following both primary and revision hip surgery in their practice. In this cohort of surgeons, of 179 reported sciatic nerve injuries, 77% were in women (80% in primary hip replacement and 69% in revision surgery), which is statistically significant.

We suggest that the wider outlet of the female pelvis causes the path of the sciatic nerve to pass more closely to the posterior wall of the acetabulum so making it more vulnerable to surgical injury. This hypothesis has been explored by measurements taken from CT scans of the pelvis and hips. Results do confirm the closer proximity of the nerve to the hip joint in women. We therefore advise increased care when performing hip replacement in women and suggest that this be mentioned as a gender linked risk when consenting patients prior to surgery.

Introduction: Developmental dysplasia of the hip (DDH) is a common cause of secondary osteoarthritis of the hip. The severity of the hip dysplasia varies considerably leading to a broad spectrum of reconstructive challenges. The custom CAD/CAM femoral stems offer a useful solution to fit and correct the abnormalities in the anatomy of the proximal femur.

Materials and Methods: The purpose of the study was to review at the functional and radiological outcome of uncemented CAD/CAM stems where the primary diagnosis is DDH. Uncemented sockets were used in all cases. Pre-operative planning consisted of a CT scan to assess the available acetabular coverage, estimate the degree of femoral anteversion and precisely evaluate the limb-length inequality. The hips were classified according to Crowe and Hartofilakidis. Patients with less than two-year follow up were excluded. The outcome was determined radiologically and using the Harris, Oxford and WOMAC scoring systems.

Results: Ninety-nine cases were identified and included in the study. The mean age of the group was 43.8 (range 26–79) with a female to male ratio was 4 to 1. The average follow up time was 5 years (range 24–118). The majority of the patients had excellent outcomes with a significant improvement in their clinical scores. The pre-operative scores were Harris Hip score 43.8 (range 9–81), Oxford 41.6 (range 19–59) and WOMAC 77.3 (range 10–120). Post operatively the scores have improved to Harris Hip Score 84.2 (range 38–99), Oxford 20.3 (range 12–48) and WOMAC 37.1 (range 24–92).

Conclusion: Total hip replacement for the sequelae of hip dysplasia is associated with high failure and complication rates. CAD/CAM stems afford a great deal of flexibility for the management of a broad spectrum of anatomical problems in these cases and provide a very useful alternative to modular prostheses. We present excellent medium term results.

Introduction: Patients with developmental dysplasia of the hip with secondary osteoarthritis are often found to have severe anatomical deformities of the hip. Total hip replacement in such patients is a complex undertaking associated with complication and failure rates. Subtrochanteric derotational osteotomy with customized uncemented total hip arthroplasty has been described to combat the problems of severe femoral anteversion. We present the medium term follow up of 12 patients where such a procedure was undertaken.

Materials and Methods: 11 female and 3 male patients with an average age of 49 (range, 32–79 years) were reviewed by an independent observer. The mean follow up was 50 months (range, 24–93 months). Patients were classified on AP radiographs according to Crowe and Hartofilakidis. All have femoral neck anteversions of greater than 45° on CT scans. The patients were followed up radiographically and clinically using the WOMAC, Oxford and Harris hip scores.

Results: 1 patient died due to unrelated causes. The average Harris hip score improved from 44 (range, 38–57) preoperatively to 88 (range, 67–94). The average WOMAC score improved from 83 (range, 45–112) pre-operatively to 36 (range, 25–72). The average Oxford score improved from 44 (range, 38–57) preoperatively to 19 (range, 14–34). Radiologically, the prosthesis appears to have osseointegrated with union of the osteotomy site in all cases and there is no evidence of implant migration or osteolysis.

Conclusion: Custom total hip arthroplasty with subtrochanteric osteotomy provides a method whereby the hip centre can be restored to its normal level, proximal bone stock is preserved and a more normal proximal femoral morphology is created. We have undertaken this procedure routinely in patients with excessive femoral anter-version and report excellent medium term clinical and radiographic results.

Introduction: An increasing number of patients present for revision hip replacement with severe bone loss. The results of cemented revision in these cases are poor. This study was conducted to determine the medium term clinical and radiological outcome of 50 consecutive revision hip replacements performed using custom femoral stems.

Materials and Method: 50 consecutive hips (49 patients) performed by the senior author between 1992 and 1995 were identified. The indications for revision were aseptic loosening in 42 cases, infection in 7 cases (6 of which were revised using a two-stage technique), and dislocation in one case. The stems are manufactured on the basis of standardised measurement films using specially developed software. The design includes proximal macrogrooves with hydroxyapatite coating, an anterior flare, a lateral flare and a collar. The average follow up was 88.4 months (range 12–111 months). All patients were evaluated radiologically and using Harris, Oxford and WOMAC hip scores.

Results: The patients were assessed by an independent observer. All had severe bone loss according to AAOS and Paprosky classifications. 5 patients died due to causes unrelated to their hip replacement, 5 were lost to follow up or did not respond to questionnaires sent. The remaining patients had average preoperative scores of HHS 40.8 (range 8–87), Oxford 43.5 (range18–56) and WOMAC 82.5 (range 40–120) and had improved to HHS 74.4 (range 19–99), Oxford 25.5(range 12–51) and WOMAC 43.8 (range 13–89).

Conclusions: The use of customised revision stems allows the implant to be tailored to the patient’s bone stock and femoral anatomy. This technique avoids the massive inventory of implants and trials needed for highly modular revision systems, but nevertheless leads to excellent bone implant apposition and interface stability. The clinical results are excellent at medium term review, and the survivorship compares very favourably with other revision series.