Abstract
BackgroundGood outcomes have been reported in revision total hip replacement with massive segmental defects using impaction bone grafting with circumferential metal meshes. However, the morphology of defects that require a mesh is poorly defined. The purpose of this study was to evaluate the effects of a variety of segmental defects on load transmission to the proximal femur under both axial and rotational loads.MethodsInitial stability of the Exeter stem was investigated in a composite bone model using three medial bone defect morphologies: Long (length 5 cm × width 2 cm), Short (2.5 cm × 2 cm), Square (3.2 cm × 3.2 cm), Square with mesh (3.2 cm × 3.2 cm defect covered with metal mesh), and with no defect as control. Specimens (5 per group) were axially loaded and internally rotated up to 20° or to failure. Strain distributions of the femora were measured using a strain gauge.ResultsAll Square group specimens failed while rotation was increasing. In the other four groups, failure was not observed in any specimens. Mean torsional stiffness in the Long (4.4 ± 0.3 Nm/deg.) and Square groups (4.3 ± 0.3 Nm/deg.) was significantly smaller than in the Control group (4.8 ± 0.3 Nm/deg.). In the medio-cranial region, the magnitude of the maximum principal strain in the Square group (1176.4 ± 100.9) was significantly the largest (Control, 373.2 ± 129.5, p < 0.001; Long, 883.7 ± 153.3, p = 0.027; Short, 434.5 ± 196.8, p < 0.001; Square with mesh, 256.9 ± 100.8, p < 0.001). Torsional stiffness, and both maximum and minimum principal strains in the Short group showed no difference compared to the Control group in any region.ConclusionsBone defect morphology greatly affected initial stem stability and load transmission. If defect morphology is not wide and the distal end is above the lower end of the lesser trochanter, it may be acceptable to fill the bone defect region with bone cement. However, this procedure is not acceptable for defects extending distally below the lower end of the lesser trochanter or defects 3 cm or more in width.
Highlights
Good outcomes have been reported in revision total hip replacement with massive segmental defects using impaction bone grafting with circumferential metal meshes
Proximal femoral bone defects have less effect on initial stem stability than with uncemented stems, so procedures equivalent to primary total hip replacement (THR) or the impaction bone grafting technique (IBG) without reinforcement are occasionally used in revision THR in cases of relatively small bone defects
Rotational test Mean torsional stiffness with torque from 5 to 65 Nm in both the Long group (4.4 ± 0.3 [95% confidence interval {CI}, 4.0 to 4.7] Nm/deg.) and the Square group (4.3 ± 0.3 [95% CI, 4.0 to 4.7] Nm/deg.) was significantly smaller than in the Control group (4.8 ± 0.3 [95% CI, 4.5 to 5.2] Nm/deg.), the stiffness did not differ among the Control group, the Short group (4.5 ± 0.2 [95% CI, 4.3 to 4.8] Nm/deg.) and the Square with mesh group (4.6 ± 0.2 [95% CI, 4.4 to 4.8] Nm/deg.) (Table 1, Fig. 3a)
Summary
Good outcomes have been reported in revision total hip replacement with massive segmental defects using impaction bone grafting with circumferential metal meshes. Revision of total hip replacement (THR) is challenging, though good clinical results have been reported [1, 2]. Proximal femoral bone defects have less effect on initial stem stability than with uncemented stems, so procedures equivalent to primary THR or the impaction bone grafting technique (IBG) without reinforcement are occasionally used in revision THR in cases of relatively small bone defects. While initial stem stability is essential in revision THR, a medial segmental defect in the femur can greatly attenuate initial stem stability [2,3,4]. Managing bone defects of the proximal femur is a central problem in revision THR
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