Update--"Big-head": the solution to the problem of hip implant dislocation?

New friction couples, initially intended to limit osteolysis risk due to debris, have enabled larger implant head diameters to be developed to resolve the problem of hip implant dislocation. The Symposium demonstrated that, whatever the configuration, increased head diameter significantly reduced the incidence of dislocation, but that none of the friction couples fulfilled the mechanical and/or biomechanical charge-book for consistently reliable use of large diameter heads. The greatest caution is therefore recommended in their implementation.

Large diameter head metal-on-metal bearings total hip arthroplasty: preliminary results

INTRODUCTION

Although the use of the metal-on-metal bearings has been validated over the long term in total hip arthroplasty (THA) for standard 28 and 32 mm diameters, and over the medium term in resurfacing procedures, the use of larger metal head size in conventional THA has not yet been extensively reported.

HYPOTHESIS

The large-diameter metal-on-metal head is beneficial in terms of implant stability without altering the result in terms of function and bone fixation compared to the standard 28 and 32 mm diameters.

OBJECTIVE

The objective was to test this hypothesis by assessing the short-term clinical and radio graphic results of a metal-on-metal large-diameter heads THA system, using cups from the resurfacing hip concept.

MATERIAL AND METHODS

We conducted a retrospective study on a continuous series of 106 uncemented acetabular cups (Durom) implanted in 102 patients (mean age, 66 years): 93 cases of primary or secondary coxarthrosis, 11 cases of aseptic osteonecrosis, one fracture of the femoral neck, and one case of rheumatoid arthritis of the hip. At 30 months of follow-up,the Harris Hip Score and the Merle d'Aubigné (PMA) score were calculated. The radiological investigation included comparison of the implant head with native head diameters, variations of acetabular center of rotation, inspection for implant migration, and search for a gap or radiolucent line.

RESULTS

The series included two post-traumatic dislocations as well as spontaneously receding tendinitis of the gluteus medius with no further recurrence. The mean Harris Hip Score improved from 49.3 preoperatively to 91.6 at the latest follow-up and the mean PMA score ranged from 12 to 17. The results were excellent for 70 cases, good for 31 cases, fair for three cases, and poor for two cases. In the last five cases, the overall results were undermined by low pain subscore,with no identifiable explanation. Restoration of the original head diameter was verified for 65 hips. No cup migration was observed. Measurement of the acetabular centre of rotation showed a mean lateralization of 1.1mm. Of the 67 immediate postoperative gaps, only two did no disappear at follow-up. Implant head diameter, cup position, and the existence of a gap were not correlated with the clinical results.

DISCUSSION

These results are comparable to 28 mm-diameter metal-on-metal heads in uncemented cups but with improved stability but without demonstrable alteration of the quality of the bone fixation. We found no mechanical or medical cause that could explain the five cases of persistent pain leading to fair or poor results. Long-term follow-up will validate these theoretical advantages in terms of wear and implant survival.

LEVEL OF EVIDENCE

IV. Retrospective series.

A comparison of the penetration rate of two polyethylene acetabular liners of different levels of cross-linking. A prospective randomised trial

We carried out a prospective randomised study designed to compare the penetration rate of acetabular polyethylene inserts of identical design but different levels of cross-linking at a minimum of four years follow-up. A total of 102 patients (102 hips) were randomised to receive either highly cross-linked Durasul, or contemporary Sulene polyethylene inserts at total hip replacement. A single blinded observer used the Martell system to assess penetration of the femoral head. At a mean follow-up of 4.9 years (4.2 to 6.1) the mean femoral head penetration rate was 0.025 mm/year (SD 0.128) in the Durasul group compared with 0.106 mm/year (SD 0.109) in the Sulene group (Mann-Whitney test, p = 0.0027). The mean volumetric penetration rate was 29.24 mm(3)/year (SD 44.08) in the Durasul group compared with 53.32 mm(3)/year (SD 48.68) in the Sulene group. The yearly volumetric penetration rate was 55% lower in the Durasul group (Mann-Whitney test, p = 0.0058). Longer term results are needed to investigate whether less osteolysis will occur.

[Successful medical treatment of post-traumatic tracheo-oesophageal fistulae (author's transl)]

Tracheo-oesophageal fistulae secondary to closed traumatic lesions of the thorax are rarely encountered, and only 38 cases have been reported in the published literature. The causal accident is usually perforation due to steering wheel projection or a crushing injury in a young subject (77% less than 30 years old) with a supple thorax, and parietal lesions are rarely observed. The initial lesion is rupture of the trachea with oesophageal confusion, usually above the level of the carina. The only diagnostic clinical sign is cough on swallowing, and diagnosis suspected on bronchoscopy is confirmed by radiological examination with a contrast medium. Urgent surgical treatment is necessary to repair the tracheal lesion. Secondary disunion may be observed (8--34). The particular characteristic of the cases presently reported was the secondary formation of a fistula after tracheal repair. Direct enteral feeding led to closure of the communication in 6 weeks.

[Internal pinning of the humerus by the supra-epitrochlear route. Apropos of 20 cases]

The authors report 20 cases of internal fixation of the humerus by the internal route, they discuss the place of internal fixation among other therapeutic methods and recall the advantages of the supratrochlear internal route, more simple to carry out and always atraumatic. This method is however only used where orthopedic treatment has failed.

[Synovial hemangioma of the knee. Report of one case (author's transl)]

Hemangioma of the synovial membrane is encountered in young adults in the form of a palpable articular tumour. The muscle wasting in the quadriceps is out of proportion with the clinical signs and should lead one to suspect the diagnosis. Lengthening of the limb on the side of the lesion by arterio-venous shunt is not rare. Histologically, hemangioma is a vascular tumour and there is the same difficulty in classification as for all vascular tumours. Synovectomy removing the tumour is the operation of choice. Relapse is possible leading to total removal of the synovial membrane. Complementary radiotherapy does not have a clearly defined place in treatment.