Clinical and dynamometric results of hip abductor system repair by trochanteric hydroxyapatite plate with modular implant after resection of proximal femoral tumors

Introduction: The capacity of the hydroxyapatite-coated trochanteric screwed plates used with modular hip implants to restore abductor system efficacy after proximal femoral tumor resection has never been assessed. We therefore conducted a retrospective study aiming to: (1) quantitatively evaluate abduction conservation on dynamometry according to use of digastric reinsertion, conserving continuity between the gluteus medius and vastus lateralis muscles, or not, and of standard versus small-offset; (2) assess radiographic trochanteric plate fixation; (3) assess functional scores; and (4) assess complications.

Hypothesis: Trochanteric reinsertion better conserves abduction strength when reinsertion is digastric.

Patients and methods: Thirty-one patients undergoing proximal femoral tumor resection between 2006 and 2016 with reconstruction by Stanmore METS™ modular implant with trochanteric plate were included. Twenty-one had digastric fixation between the gluteus medius and vastus lateralis and 10 had simple trochanteric fixation without digastric continuity. Abduction strength was compared between sides on dynamometer. Sixteen patients had full assessment of muscle strength, by a single observer; there were 8 deaths, 5 patients lost to follow-up, and 2 cases of material removal.

Results: Abduction strength conservation versus the contralateral side was 55.2±23.3% (range, 5.8-86.1%): 66.6±13.0% (46.4-86.1) with versus 36.0±24.7% (5.8-63.2%) without digastric continuity (p=0.01); severe limp rate was 4/21 when digastric continuity was preserved (19%) versus 6/10 (60%) (p=0.04), and radiologic trochanteric reinsertion stability rate was 19/21 (90%) versus 4/10 (40%) (p=0.005). Standard femoral offset conserved greater abduction strength: 64.9±20.0% versus small-offset 45.4±23.2% (p=0.05). Toronto Extremity Salvage Score (TESS) was 89±9.4%, and Musculoskeletal Tumor Society (MSTS) score 75.4±5.4%. There were 6 complications (19%): 4 infections, 1 dislocation, and 1 plate removal; the single dislocation (3%) was in the digastric conservation group. TESS (90.7±7.8% vs 88.3±4) and MSTS score (75.6±4.0% vs 75.1±3.7) and complications [4/21 (19%) vs 2/10 (20%)] did not differ according to digastric or non-digastric reinsertion (p=1).

Conclusions: Abduction strength with a modular implant using a hydroxyapatite-coated trochanteric plate was better conserved by digastric trochanteric reinsertion, resulting in less limping, although the complications rate and functional scores were unaffected. Longer term assessment is needed to confirm this conservation of abduction strength.

Level of evidence: IV, retrospective study without control group.