A predictive radiological analysis of short stems versus both shortened and long stems in primary hip replacement: A case-control study of 100 cases of Metha versus ABG II and Omnifit HA at 2-8years' follow-up

INTRODUCTION

Short hip stems, intended to conserve bone stock and ensure a more physiological distribution of stress in the femur under loading, are meeting with renewed interest. Radiologic semiology is not known exactly, particularly in relation to conventional implants; we therefore conducted a case-control study of 3 types of implant differing only in stem length: short, shortened or long. The aim was: (1) to compare radiographic aspects, (2) to attempt to systematize medium-term radiologic status for the 3 types, and (3) to assess the impact of radiographic aspect on loosening and revision rates.

HYPOTHESIS

The short Metha stem is better adapted to the recipient bone than longer stems, without sacrificing stability.

MATERIAL AND METHODS

A prospective series comprising the first 100 selected cases of hip replacement using the short Metha stem was compared to two other series of 100 "long" (Omnifit HA) and 100 "shortened" (ABG II) stems at comparable follow-up: 4.05±1.44years (range: 2-8years) for Metha, 4.48±0.97years (range: 2-8years) for Omnifit, and 4.75±2.07years (range: 2-8years) for ABG II. Selection criteria in this initial phase were very strict: young age and/or high activity level, with good bone stock and femoral morphology suited to fitting a Metha stem (no "stovepipe" or "champagne-flute" femurs), for which 12.8% of primary hip replacements were selected. Matching was performed by sampling on criteria of age, gender, body-mass index and etiology. Radiographic parameters were compared between the short stem group and the two control groups and classified according to Engh-Massin score (10 points for fixation and 17 for stability).

RESULTS

The short Metha stem provided excellent fixation scores: 7.65/10, versus 7.16 (P=0.003) and 5.92 (P=0.0001) for ABG II and Omnifit, respectively. Likewise, stability was scored 14.23/17 for Metha, vs. 14.51 (NS) and 11.83 (P=0.0001) respectively, and the total score was higher for Metha (21.88/27) than ABG II (21.67; P=0.03) or, more particularly, Omnifit (17.83; P=0.0001). The Metha stem was never associated with thigh pain or periprosthetic fracture. 8-year survival was 100%, without significant difference with respect to ABG II (100%; NS) or Omnifit (98.8%; 95% CI: 0.964-1; NS).

DISCUSSION

The apparent radiologic superiority of the short Metha stem requires long-term confirmation in non-selected series. Meanwhile, Metha can be asserted to have demonstrated optimal compromise between lasting bone anchorage and respect of bone physiology under loading at medium term.

LEVEL OF EVIDENCE

III, case-control study.

A two step synthesis of a key unit B precursor of cryptophycins by asymmetric hydrogenation

A novel highly enantioselective two step access to a unit B precursor of cryptophycins in good yields from commercially available starting materials has been developed. The key step is an asymmetric hydrogenation using the commercially available [(COD)Rh-(R,R)-Et-DuPhos]BF₄ catalyst. The synthetic route provides the advantage of less synthetic steps, proceeds with high yields and enantioselectivity, and avoids hazardous reaction conditions.

[Results of lumbar and lumbosacral fusion: clinical and radiological correlations in 113 cases reviewed at 3.8 years]

PURPOSE OF THE STUDY

Spinal fusion requires the use of hardware for reduction and stabilization. We present the clinical and radiological behavior of a population of patients with lumbar and lumbosacral spinal fusion.

MATERIALS AND METHODS

Between 1990 and 1992, 113 patients were operated for lumbar and lumbosacral fusion. Mean age of the population was 43 years and mean follow-up was 3.8 years. Most of the fusions were L4-S1 fusions. 56% of the patients had a previous surgery. Thirteen patients in the series were reoperated and analyzed separately. In the majority of the cases, the indication for surgery was back pain with or without leg pain. Diagnoses were: spondylolisthesis, discopathy, scoliosis, and pseudoarthrosis. The spine was fused and reduced using two lordotic rods. Peroperative and postoperative lordosis were calculated on X-rays. Clinical results were analyzed with the Beaujon-Lassale score.

RESULTS

Mean improvement was significantly better for spondylolisthesis than for other pathologies (85.6% versus 77.1%). Returning to work was possible for 85.5% of those with improvement and was not possible for 69.8%. The gain achieved in lordosis at surgery was lost at last follow-up. The lordosis of the construct appeared to protect against the development of discopathies above and below the construct. Discopathis led to a poor score. The rate of non-union was 7.9%, the rate of repeated surgery 6.1% and the rate of hardware removal 23.8%. At last follow-up, improvement was achieved in 45.6% of the 13 patients of the series who had repeat surgery.

DISCUSSION

The results in our series are similar to those reported by others. Lumbar lordosis is an important factor: if lost, more interbody fusions may be subsequently required. Diagnosis of non-union is difficult and reoperation is the only sure manner to prove it by applying distraction-compression manoeuvres on the screws. All non-unions presented were symptomatic; incidence in the series was thus probably higher. Non-union and reoperation with a longer fusion are perhaps correlated with insufficient elasticity in the osteosynthesis. Optimal rod elasticity is a factor which remains to be defined.

CONCLUSION

Clinical results of lumbar and lumbosacral fusions are not unsatisfactory, but in our series almost one patient out of three had to be reoperated. One of the reasons for so many reoperations is certainly hardware rigidity. Hardware was not removed without testing the fusion as this is the only means of sure diagnosis of non-union. Reoperation should not be considered a failure in this difficult surgery of back pain which requires long-term surgical follow-up.