Purpose of the study: This prospective study was conducted to analyze the mechanisms of gait compensation in patients with painful hip and to search for correlations with preoperative clinical and radiographic findings.

Material and methods: Optoelectronic and multicomponent force-plate datas were used to calculate joint motion, moments and intersegmental forces for 26 patients with unilateral hip pain and 20 normal age and sex-matched patients. Height was similar in the two groups but mean weight in the study group (83 kg) was greater than in the controls (68 kg). The preoperative Harris score was 53 in the study group and 16 patients had a permanent flexion contracture of the knee (mean 15°, range 5–30°). Radiographically, there were 22 cases of osteoarthritis hip disease and 4 cases of necrosis.

Results: Gait analysis showed a significant 0.66 ± 0.06 m (12 p. 100) reduction in step length. Patients who had severe hip pain walked with a decreased dynamic range of motion (18 ± 5°, p < 0.0001) with a curve reversal as they extended the hip. They also reduced dynamic range of motion of the knee and ankle. Patients who presented a reversal in their dynamic hip range of motion had a greater passive flexion contracture and a greater loss in range of motion during gait than those with a smooth regular pattern (p < 0.0001). Patients with hip pain walked with significantly decreased external extension, adduction, and internal and external rotation moments (p < 0.0001). They also unloaded the ipsilateral knee and ankle. The decreased hip extension moment was significantly correlated with an increased level of pain (p < 0.0001). There was no correlation with radiological findings.

Discussion: Reversal of dynamic hip range of motion was interpreted as a mechanism to increase effective hip extension during stance phase through increased anterior pelvic tilt and lumbar lordosis.

Conclusion: Patients with painful hip walked with a manner that was asymmetric. These gait modifications were related to hip limitation in passive motion and pain. Patients with flexion contracture adopted a compensatory gait mechanism. This study confirms relation between hip pain and forces across the hip joint.

Interfacial membranes collected at revision from 11 failed uncemented Ti-alloy total hip replacements were examined. Particles in the membranes were characterised by electron microscopy, microchemical spectroscopy and particle size analysis. Most were polyethylene and had a mean size of 0.53 micron +/- 0.3. They were similar to the particles seen in the base resin used in the manufacture of the acetabular implants. Relatively few titanium particles were seen. Fragments of bone, stainless steel and silicate were found in small amounts. Most of the polyethylene particles were too small to be seen by light microscopy. Electron microscopy and spectroscopic techniques are required to provide an accurate description of this debris.