Resurfacing hip arthroplasty better preserves a normal gait pattern at increasing walking speeds compared to total hip arthroplasty.

Background and purpose - Gait analysis performed under increased physical demand may detect differences in gait between total (THA) versus resurfacing hip arthroplasty (RHA), which are not measured at normal walking speed. We hypothesized that patients after RHA would reach higher walking speeds and inclines compared with THA. Additionally, an RHA would enable a more natural gait when comparing the operated with the healthy contralateral hip. Patients and methods - From a randomized controlled trial comparing THA with RHA with at least 5 years' follow-up patients with a UCLA score of more than 3 points (n = 34) were included for an instrumented treadmill gait analysis. 25 patients with a unilateral implant (primary analysis-16 THA versus 9 RHA) and 9 patients with a bilateral implant (sub-analysis-n = 5 RHA + THA; n = 4 THA + THA). Spatiotemporal parameters, ground reaction forces, and range of motion were recorded at increasing walking speeds and inclines. Functional outcome scores were obtained. Results - At a normal walking speed of 1.1 m/s and at increasing inclines no differences were recorded in gait between the 2 groups with a unilateral hip implant. With increasing walking speed the RHA group reached a higher top walking speed (TWS) (adjusted difference 0.07 m/s, 95% CI -0.11 to 0.25) compared with THA. Additionally, RHA patients tolerated more weight on the operated side at TWS (155 N, CI 49-261) and as such weight-bearing approached the unaffected contralateral side. For the RHA group a "between leg difference" of 8 N (CI 3-245) was measured versus -129 N (CI -138 to -29) for THA (adjusted difference 144 N, CI 20-261). Hip flexion of the operated side at TWS was higher after RHA compared with THA (adjusted difference 8°, CI 1.7-14). Interpretation - In this study RHA patients reached a higher walking speed, and preserved a more normal weight acceptance and a greater range of hip flexion against their contralateral healthy leg as compared with patients with a THA.

Bone mineral density changes in the graft after acetabular impaction bone grafting in primary and revision hip surgery.

Background and purpose - Impaction bone grafting (IBG) is an established method in hip revision surgery to reconstruct loss of bone stock. There is limited knowledge concerning the actual bone remodelling process within the allograft. We investigated with repeated bone mineral density (BMD) measurements the biological process of bone remodelling in the allograft in vivo. We hypothesized that an initial decrease in BMD would be followed by an increase towards baseline values. Patients and methods - Dual-energy X-ray absorptiometry (DXA) was used to measure BMD values in 3 regions of interest (ROI) in 20 patients (average age at surgery 70 years, 11 males) after an acetabular reconstruction with IBG and a cemented cup. A postoperative DXA was used as baseline and DXA was repeated at 3 and 6 months and at 1 and 2 years. The Oxford Hip Score (OHS), the 12-Item Short Form Health Survey (SF12), and a 0 to 100 mm visual analogue scale (VAS) for pain and satisfaction were obtained simultaneously. Results - The overall mean BMD in the IBG regions increased significantly by 9% (95% CI 2-15) at 2 years' follow-up. In the cranial ROI BMD increased 14% (CI 6-22), whereas the BMD in the medial and caudal ROI showed an increase of 10% (CI 1-18) and 4% (CI -6-16), respectively. The OHS, SF12-mental, and VAS for pain all improved statistically significantly 2 years after surgery, with a mean VAS for satisfaction of 77 (CI 63-90) out of 100 points. The SF12-physical showed non-significant improvement. Interpretation - The BMD in the allograft gradually increased after IBG for acetabular reconstruction arthroplasties, particularly in the cranial ROI. An initial decrease in the BMD was not encountered. These BMD changes, as proxy measurements for bone remodeling, may indicate progressive apposition of vital new host bone in the grafted area.

High incidence of intraoperative calcar fractures with the cementless CLS Spotorno stem.

INTRODUCTION: This study reports on the incidence of intraoperative calcar fractures with the cementless Spotorno (CLS) stem, and the potential role of a learning curve and implant positioning is investigated. METHODS: After introduction of the CLS stem, 800 consecutive cementless total hip arthroplasties (THA) were analyzed. The incidence of calcar fracture in the first 400 THA was compared with the second 400 THA, in order to study a potential learning curve effect. According to the instruction for users, varus positioning of the stem was avoided and a femoral neck osteotomy was aimed relatively close to the lesser trochanter since these are assumed to be correlated with calcar fractures. Implant positioning (neck-shaft angle, femoral offset and osteotomy-lesser trochanter distance) was measured on postoperative pelvic radiographs of all THA with calcar fractures and 100 randomly selected uncomplicated control cases. RESULTS: Seventeen (2.1%) intraoperative calcar fractures were recorded. The incidence of calcar fracture differed between the first 400 THA (n = 11) and the second 400 THA (n = 6). This difference was not statistically significant (p = 0.220); however, these numbers indicate a trend toward a learning effect. No significant difference in stem positioning nor the height of the femoral neck osteotomy was measured between THA with a calcar fracture (n = 17) and the control cases (n = 100). CONCLUSIONS: We report on a high incidence of intraoperative calcar fractures with the use of a CLS stem. The risk for calcar fractures remains clinically significant even after adequate implant positioning in the hands of experienced hip surgeons. Surgeons should be aware of this implant related phenomenon and be alert on this phenomenon intraoperatively.

Changes in bone mineral density and femoral neck narrowing in the proximal femur three to five years after hip resurfacing versus conventional total hip arthroplasty.

We studied whether bone mineral density (BMD) is preserved without significant femoral neck narrowing (FNN) after hip resurfacing (RHA) (n=42) versus small diameter metal-on-metal total hip arthroplasty (MoM THA) (n=40). In this three to five year randomized trial BMD was measured in the calcar with dual energy absorptiometry (DXA) preoperatively, at three and six months, one, two, three and five years postoperatively. Four additional BMD regions of interest (ROIs) and femoral neck narrowing (FNN) were measured after RHA. BMD in the calcar increased to 107% (P<0.001) at one year and remained stable. Additional ROIs in the femoral neck and trochanter-area BMD changes fluctuated between 99.9% and 104.1%. FNN was minimal with a mean of 1.3% at three years. After THA BMD decreased in the calcar to 80% at one year (P<0.001) and stabilized. This bone stock preserving nature of RHA must be weighed against potential disadvantages caused by specific metal-on-metal bearing problems.

Modular necks in primary hip arthroplasty without anatomical deformity: no clear benefit on restoration of hip geometry and dislocation rate. An exploratory study.

Modular necks were introduced in total hip arthroplasty (THA) to improve restoration of hip-geometry and reduce dislocation-rates. This presumed advantage was evaluated retrospectively for patients with arthritis in otherwise anatomically normal hips. Restoration of hip-geometry was assessed on preoperative and postoperative calibrated radiographs in 95 consecutive primary THAs with a modular neck design and compared with 95 match controlled THAs with a similar monoblock stem. No significant differences were seen in restoration of body moment arm, leg length and cupangle. Offset restoration revealed a borderline significant difference (P = 0.48) with higher values for the monoblock stem. In both groups 4 dislocations within one year were encountered. In this study modular necks did not reveal a clear benefit in restoring hip geometry and dislocation rate after straightforward THA.

Excessive polyethylene wear and acetabular bone defects from standard use of a hooded acetabular insert in total hip arthroplasty.

PURPOSE: In total hip arthroplasty (THA) the use of a polyethylene (PE) insert with a hooded rim can be considered to reduce dislocation risks. This benefit has to be balanced against the potential introduction of impingement of the femoral component on this rim. We present a case series of early acetabular revisions for excessive PE wear and acetabular bone defects from overuse of such a hooded rim insert. MATERIAL AND METHODS: Twenty-eight patients with 34 consecutive early acetabular revisions were evaluated on failure mechanism. One type of implant was used in all cases. Standard pelvic radiographs and pre-operative CT scans were used to quantify PE wear, implant positioning and acetabular bone defects. RESULTS: An acetabular revision with impaction grafting was performed in all cases with a mean cup survival of ten years (range 1.3-19.3). No concurrent stem revisions were necessary. Overall implant positioning was adequate with a mean cup inclination of 45° (range 39-57) and anteversion of 25° (range eight to 45). The mean PE wear was 0.24 mm/year (range 0.00-1.17). The mean acetabular bone defect on pelvic CT scans was calculated as 352 mm² (range zero to 1107) and 369 mm² (range zero to 1300) in the coronal and transversal planes, respectively. A hooded acetabular insert was retrieved in all cases and profound PE wear, typically from the posterior hooded rim, was encountered. CONCLUSION: The use of hooded acetabular inserts may be considered to improve implant stability intra-operatively. This case series clearly presents that together with these devices, component impingement with concordant complications such as accelerated PE wear may be introduced. Standard use of these stabilizing inserts should thus be avoided.

Increase in physical activity after resurfacing hip arthroplasty is associated with calcar and acetabular bone mineral density changes.

PURPOSE: Bone preservation is an important advantage of the resurfacing hip arthroplasty (RHA) concept. We hypothesised that patients' increase in physical activity level after RHA would positively relate with periprosthetic bone mineral density (BMD) changes and thus facilitate bone preservation. METHODS: BMD-changes were prospectively recorded in 38 patients after RHA. Dual-energy absorptiometry was used to quantify BMD-changes in 6 periprosthetic regions of interest preoperatively, at 6 months, 1, 2 and 3 years postoperative. The effect estimates of patients' physical activity, according to their Harris Hip Score (HHS) and University of California at Los Angeles (UCLA) Activity Score, on these BMD changes were assessed in linear mixed models. RESULTS: The UCLA (coefficient = 0.02 (95% CI, 0.010-0.034); p<0.001) and HHS (coefficient = 0.002 (95% CI, 0.001-0.003); p<0.001) were associated with the BMD in the calcar region. As for BMD changes in the femoral neck only the HHS was associated (coefficient = 0.0006 (95% CI, <0.0001-0.001); p = 0.04). Both the UCLA and the HHS were inversely associated with BMD in the medial acetabular region (UCLA: coefficient = -0.02 (95% CI, -0.038 to -0.007); p = 0.005, HHS: coefficient = -0.002 (95% CI, -0.003 to -0.001), the same accounted for the HHS to BMD-change cranial to the acetabulum (-0.001 [95% CI, -0.0018 to -0.0001]; p = 0.03). For the caudal acetabular and femoral subtrochanteric region no relation with BMD-changes was found. CONCLUSIONS: The increase in activity scores after RHA was indeed associated with an increase in BMD in the calcar region, however unexpectedly also with a BMD decrease on the acetabular side. Stress shielding from the implant is the most likely causative factor.