Introduction: Proximal porous coating for cementless fixation of femoral stems enjoys increasing popularity. We report on the intermediate to long-term results with a circumferentially proximally coated stem with a non-porous cylindrical diaphyseal portion. The smooth stem provides temporary rotational stability so that proximal bony ingrowth can occur.

Materials and methods: Between 1991 and 1994, 124 Multilock stems were implanted in 101 patients. Patients were followed prospectively and re-evaluated at a minimum five years postop (range 60 to 117 months) by an author other than the surgeon. Four patients (5 hips) were lost to follow-up. Five patients (6 hips) had died. Twenty-six patients (30 hips) had phone interviews more than five years after surgery, but no radiographs as they refused to return for followup. None of these patients had required additional surgery and all were extremely satisfied with their outcomes. Sixty-six patients (83 hips) had clinical and radiographic followup at minimum five-years post-op. This report focuses upon this last group.

Results. The average age at surgery was 53.8 years (range, 27–75). The average follow-up was 78 months (range, 60–117). The average Harris Hip Score was 93 (range, 52–100). One stem had been revised for loosening (1%), and none were radiographically loose. Eight patients (9.6%) had minimal thigh pain related to excessive activity. These patients required mild analgesics only. Eighty-two stems (99%) achieved bony ingrowth. Twenty-nine stems (35%) had minimal osteolysis limited to Zones 1 and 7. There were no cases of diaphyseal lysis. Radiolucent lines adjacent to the porous coating were evident in 3 stems (3.6%), and along smooth portions in 20 stems (24%). No radiolucent lines were progressive or divergent. Some degree of stress shielding in the proximal metaphysis was evident in 52 hips (63%), but only 2 had cortical resorption.

Discussion and conclusion. Given the young age and high activity level of this cohort of patients, the Multilock stem has fared extremely well. Loosening and revision rates were very low, and distal osteolysis had not occurred. Bony fixation occurred reliably. Proximal stress shielding remains concerning and further follow-up will determine whether this becomes clinically significant. Lastly, patient function and satisfaction were high. In conclusion, the Multilock proximally porous-coated stem can be expected to perform well in the intermediate to long-term in young, active patients.