Proximal femoral osteotomy as the primary operation for young adults who have osteoarthrosis of the hip.

We report the results of proximal femoral osteotomy that was performed to treat osteoarthrosis in twenty-three consecutive young adults (twenty-five hips) who had a mean age of thirty-eight years (range, eighteen to fifty-three years). The mean duration of follow-up was seven years (range, two to twelve years). With conversion to a total hip replacement as the end point, the rate of survival at twelve years was 67 per cent (95 per cent confidence interval, 37 to 88 per cent). Four hips (16 per cent) were converted to a total hip replacement at a mean of eight years after the osteotomy. For the patients who did not have conversion to a total hip replacement, the mean score for pain, according to the system of Merle d'Aubigné and Postel as modified by Charnley, improved from 3.4 points preoperatively to 5.1 points postoperatively, the mean score for walking ability improved from 3.9 to 4.7 points, and the mean score for range of motion improved from 3.2 to 4.2 points. These results compare favorably with those following other forms of operative treatment of osteoarthrosis of the hip in young adults. In addition, the osteotomy does not preclude subsequent replacement arthroplasty if one is necessary.

Acetabular morphology and resurfacing design.

The bony surfaces of 18 archaeological hemipelves were scanned using a 3D laser surface scanner and CyDir software on a Silicon Graphics workstation. The acetabular area was selected and point data from the approximately spherical bone surface saved. These data were input to a MATLAB routine that calculated the radius and centre of the best-fit sphere. The goodness of fit was estimated using the mean and standard deviation of the distance of the bone surface points from the sphere surface. Eight points, at approximately equal distances around the acetabular rim, were selected with reference to bony landmarks. A plane containing three of these points served as an orientation reference plane. The vectors joining the eight rim points to the centre of the best-fit sphere were found. The angles between these vectors and the normal to the reference plane were calculated. Paired angles were summed to give the angle subtended by the acetabular rim in four directions. The overall mean angle was 158 degrees (range of mean angles 145 degrees -173 degrees ). The largest individual angles, some exceeding 180 degrees, were in the superior-inferior direction, while the mean angle in the anterior-posterior direction, i.e. that controlling flexion-extension, was 152 degrees. Males had larger subtended angles than females, although the difference was not statistically significant. Simulated reaming increased all angles by approximately 10 degrees. The subtended angles are important parameters in the design of the acetabular component of a hip replacement and particularly important in resurfacing hip replacement when the volume available is tightly constrained.

Long-term results of revision hip arthroplasty. Survival analysis with special reference to the femoral component.

We report a clinical and radiological survival analysis of 148 consecutive revisions of hip arthroplasties. All patients referred were offered revision if it was indicated and they were medically fit. About one-third (32%) had had at least one previous revision, and about one-third had an established deep infection. The revisions were performed in ultra-clean air with body-exhaust suits. The usual method of fixation was by contained and pressurised cement of standard viscosity, to which appropriate antibiotics had been added in infected cases. Some patients had cementless revision. Clinical failure meant that one or both of the implants had been removed; radiological failure was assessed from serial radiographs. The clinical survival at ten years was 95%. The Merle D'Aubigné and Postel rating for pain improved from a mean of 2.9 to 5.2; and in Charnley group A and B cases, walking ability improved from 2.3 to 4.3. In contrast to some reports we also found good radiological survival; this was 90.5% for cemented femoral stems. Isoelastic revision stems inserted without cement gave poor results.

Arthroscopic, open partial, and total meniscectomy. A comparative study.

The results of three different types of meniscectomy have been compared in 219 knees, 71 treated by arthroscopic partial meniscectomy, 45 treated by open partial meniscectomy, and 103 treated by open total meniscectomy, with a mean follow-up of 4.3 years. Knees which had undergone previous operations or had other simultaneous operative procedures or ligamentous damage were excluded. Knees with chondromalacia were included provided that this did not amount to frank osteoarthritis. Simple indicators were used for the rate of early recovery from the operation, and the Tapper and Hoover scale was used to record the symptomatic results in the longer term. It was found that knees treated by arthroscopic partial meniscectomy did considerably better than the others by all the criteria used. In most parts of the study there was a clear gradation between the results of the three types of treatment: arthroscopic techniques did better than open operations, and partial meniscectomy did better than total meniscectomy.

The below-elbow myo-electric prosthesis. A comparison of the Otto Bock myo-electric prosthesis with the hook and functional hand.

The place of the myo-electric prosthesis in below-elbow amputees has been reviewed. Forty-three patients were seen and all possessed both a myo-electric prosthesis and a standard artificial limb. Nearly half the patients used the newer device almost all the time at work and many of these wore it for the majority of their waking hours. Its use at work was mainly related to the patient's type of job and here in turn there was concern about damaging the device. It is suggested that acceptance would be further increased if greater attention were paid to the durability of the arm and its glove. Criteria for prescription and future developments are discussed.

A biomechanical study of the effects of growth hormone in experimental fracture healing.

In 65 mature Wistar rats a Kirschner wire was introduced into the medullary cavity of each femur. A closed transverse mid-shaft fracture of one femur was produced by a three-point bending technique. Subsequently the mechanical characteristics of the healing fracture, including the torque and angle of twist required to take the callus to its yield point and to ultimate failure, were compared with those for the opposite femur of each rat. Controls were killed in groups at two, three, four, five and seven weeks. Test animals were given bovine growth hormone in a daily dose of five milligrams before being killed in groups at two, three and four weeks. A significant increase in torque index was found in the two-week group of test animals but not in subsequent groups. No evidence was found that growth hormone given alone could produce an overall shortening of the healing time in fresh fractures.

Sequential haematogenous infection of bilateral cementless total hip replacements.

We report a patient with bilateral uncemented total hip replacements in whom a deep infection on the second side may have been caused by a transient bacteraemia associated with a revision operation for deep infection on the first side. Both hips were successfully treated by one-stage exchange.

Effects of acetabular resurfacing component material and fixation on the strain distribution in the pelvis.

A 3D finite element (FE) model of an implanted pelvis was developed as part of a project investigating an all-polymer hip resurfacing design. The model was used to compare this novel design with a metal-on-metal design in current use and a metal-on-polymer design typical of early resurfacing implants. The model included forces representing the actions of 22 muscles as well as variable cancellous bone stiffness and variable cortical shell thickness. The hip joint reaction force was applied via contact modelled between the femoral and acetabular components of the resurfacing prosthesis. Five load cases representing time points through the gait cycle were analysed. The effect of varying fixation conditions was also investigated. The highest cancellous bone strain levels were found at mid-stance, not heel-strike. Remote from the acetabulum there was little effect of prosthesis material and fixation upon the von Mises stresses and maximum principal strains. Implant material appeared to have little effect upon cancellous bone strain failure with both bended and unbonded bone-implant interfaces. The unbonded implants increased stresses in the subchondral bone at the centre of the acetabulum and increased cancellous bone loading, resembling behaviour obtained previously for the intact acetabulum.

Distal femoral plug migration with cement pressurization in revision surgery and a simple technique for its prevention.

The notes and radiographs of a consecutive series of 83 hip revisions were studied. In 69 hips, a cemented femoral component was used in which the cement was pressurized and the canal was blocked by an intramedullary plastic plug. It was found that distal migration of this plug occurred very frequently and, in 14 hips (20%), the migration was considered severe. The causes and implications of this are discussed, and a simple technique for preventing the problem is described.

Long-term results of arthroscopic partial meniscectomy.

Detailed analysis of a series of 99 arthroscopic partial meniscectomies with a minimum follow-up time of 2.1 years (mean, 3 years; maximum, 4.5 years) showed that the spectacularly good early results were maintained in the longer term. Group I knees (67) had no previous surgery or ligamentous insufficiency, but those with chondromalacia were included. The remaining knees were designated Group II and analyzed separately. Group I showed 51.5% excellent and 39% good results, using criteria based on those of Tapper and Hoover. When only results in bucket handle tears were considered, 73% were excellent and 19% were good. Results in Group I also depended on the presence or absence of chondromalacia. Results in Group II were poorer than in Group I, but were still satisfactory in 67% of knees, although many had a torn anterior cruciate ligament of frank osteoarthritis. The arthroscopic technique should, where possible, become the standard method of treatment if patients require meniscectomy.

Tensile mechanical properties of polyacetal after one and six months' immersion in Ringer's solution.

The engineering polymer polyacetal (also known as polyoxymethylene) has a long history of clinical use including in the femoral component of the Freeman all-polymer knee replacement. The polymer is a promising material for novel applications including the femoral component of hip resurfacing prostheses. However, no work following the effect on mechanical properties of extended immersion in the physiological environment has been reported. Samples of five grades of polyacetal were obtained and tested on an MTS Bionix 858 at 37 degrees C in physiological saline. Three groups of specimens were tested: "as received"; immersed in Ringer's solution at 37 degrees C for one month; immersed in Ringer's solution at 37 degrees C for six months'. While there were negligible reductions in the ultimate tensile strengths, the Young's moduli of all polymer grades showed significant reductions (p < 0.01) of up to 19.5% following one months' immersion. There were negligible changes in ultimate tensile strength and stiffness between one and six months' immersion, however some polymers showed a small, but significant (p < 0.05) increase in stiffness. The percentage elongation and true stress for plastic instability showed negligible changes following immersion for one and six months'. These results encourage the use of polyacetal in load-bearing orthopaedic applications.

An in vitro study of a new design of acetabular cement pressurizer.

Aseptic loosening of the acetabular component remains one of the limiting factors in the long-term success of total hip arthroplasty. Cement pressurization has been shown to improve fixation. A new pressurizer has been designed that seals around the rim of the acetabulum and covers the transverse ligament notch with a flap. The results of in vitro testing of this device are presented and compared with those of pressure generated by insertion of an acetabular cup. The pressurizer allowed sustained, uniform cement pressurization. Peak pressures with the new pressurizer were 180 kPa at both the iliac region of the rim and the pole of an instrumented model acetabulum, compared with 55 kPa at the rim and 120 kPa at the pole on cup insertion. Pressures were maintained in the range of 80-90 kPa. The flap was effective in preventing cement leakage from the notch, and pressures were higher than when the flap was absent. Cup insertion alone gave only transient pressurization, substantially less near the rim of the acetabulum than at the pole. Peripheral pressurization may be significant in producing secure local fixation at the rim of the acetabulum, in particular in the region of the ilium (Charnley zone 1), where radiolucencies are most commonly observed and where stresses in the implanted acetabulum are highest. Improved rim fixation may also play a role in preventing the ingress of wear debris.

In vivo measurement of acetabular cement pressurization using a simple new design of cement pressurizer.

Aseptic loosening of the acetabular component remains a limiting factor in the long-term success of total hip replacement. An instrumented pressurizer has been designed to allow the intraoperative measurement of acetabular cement pressurization, which is known to contribute to implant fixation. Average intraoperative cement pressures in 16 operations performed by 2 surgeons were 49 +/- 17 kPa (6.4 +/- 2.3 psi) and 47 +/- 17 kPa (6.2 +/- 2.2 psi), and peak pressures were 76 +/- 5 kPa (10.0 +/- 0.6 psi) and 93 +/- 15.kPa (12.2 +/- 1.9 psi), comparable to previous work in vitro. The pressurization required for optimal cement penetration into cleaned low-density cancellous bone is reported to be of the order of 35 to 50 kPa (4.6-6.6 psi) for 30 to 60 seconds, and the present data show that this is attainable in vivo using a simple device.