An in vitro study of the strain distribution in human femora with anatomical and customised femoral stems

Purpose The number of candidates for a total hip arthroplasty (THA) is steadily increasing, while the average patient age is decreasing for primary THA. The rise in THA is mainly due to excellent clinical outcomes and the extended longevity of modern implants. Short stem arthroplasties with predominantly metaphyseal fixation such as the Metha® stem are suggested for young patients. It is hypothesised that the more physiological load transfer of these devices reduces stress shielding, which in turn may reduce the risk of aseptic loosening. However, patients with femoral deformities often require a deviation of the resection height. To this end, our aim was to evaluate how resection height influences strain patterns in order to characterise possible limits for short stem implantation. Methods Biomechanical testing using ten strain gauges on synthetic bone illustrated the strain patterns of three different resection heights (0, +5 and +10 mm) for the Metha stem. Results The greatest differences in strains were displayed at the "high" (most proximal) resection height (+10 mm) when compared to the non-implanted strain pattern. At the medial calcar, the strain was 143 % for +10 mm, 96 % for +5 mm and 94 % for 0 mm. Overall, discrepancies were less for deeper resections. Conclusions The deeper the resection, the more similar the strain patterns are when compared to a non-implanted synthetic bone. Changes in strain patterns are induced by variation in the varus/valgus positioning of the implant and by different offsets.

International Orthopaedics (SICOT)

Section: Discussionsupporting

confidence: 92%

The influence of resection height on proximal femoral strain patterns after Metha short stem hip arthroplasty: an experimental study on composite femora

Floerkemeier

Gronewold

Berner

et al. 2012

“…Studies support the idea that the ultrashort stem relieves pain and restores function comparable to conventional stems at short-and long-term followup [10,17,19,35]. Thigh pain is believed to be related to stem design and implant stiffness [3,5,6,9,24,30,37]. The normal modulus of elasticity of cortical bone is less than 20 GPa [5], whereas most conventional metal implants occupying the diaphysis have a modulus of elasticity between 80 and 200 GPa [30,37]; therefore, an ultrashort or tapered, polished intramedullary stem is one way to preserve femoral elasticity and avoid thigh pain.…”

Section: Discussionmentioning

confidence: 92%

“…Thigh pain is believed to be related to stem design and implant stiffness [3,5,6,9,24,30,37]. The normal modulus of elasticity of cortical bone is less than 20 GPa [5], whereas most conventional metal implants occupying the diaphysis have a modulus of elasticity between 80 and 200 GPa [30,37]; therefore, an ultrashort or tapered, polished intramedullary stem is one way to preserve femoral elasticity and avoid thigh pain. The absence of thigh pain in all but two patients in the ultrashort stem group may be attributed to rigid axial and torsional stability in the proximal femur and maintaining a normal modulus of elasticity in the diaphysis by absence of the distal stem.…”

Section: Discussionmentioning

confidence: 99%

Ultrashort versus Conventional Anatomic Cementless Femoral Stems in the Same Patients Younger Than 55 Years

Park

Clinical Orthopaedics &Amp; Related Research

2016

Background Because the clinical and radiographic performance of an ultrashort anatomic cementless stem has been investigated in only two randomized controlled studies, well-designed trials should aim for a thorough comparison of the outcomes of ultrashort anatomic cementless and conventional anatomic cementless stems. Questions/purposes The purposes of this study were to compare (1) the clinical results, including Harris hip score, thigh pain, and WOMAC index score, (2) radiographic results, (3) bone mineral density; and (4) proportions of patients undergoing revision of a THA using an ultrashort anatomic cementless stem versus a conventional anatomic cementless stem in the same patients who underwent bilateral sequential THAs under the same anesthetic. Methods Two hundred patients (mean age, 53 years; range, 26-54 years) who underwent bilateral sequential THAs received an ultrashort anatomic cementless stem in one hip and a conventional anatomic cementless stem in the contralateral hip. From January 2004 to December 2005, we performed 524 same-day bilateral short and conventional anatomic cementless THAs in 262 patients, of whom 212 (81%) participated in this study. Five patients were lost to followup before 2 years, five were lost between 2 to 10 years, and two were lost between 10 to 13 years, leaving 200 patients. Patients who had end-stage bilateral hip disease and were younger than 55 years were selected for inclusion. The predominant diagnoses were osteonecrosis (118 patients, 59%) and osteoarthritis (44 patients, 22%). One hundred thirty-eight were men and 62 were women. At the time of each followup, the patients were assessed clinically and radiographically. In addition, each patient completed the WOMAC and the University of California Los Angeles (UCLA) activity scores. The minimum followup was 10 years (mean, 11.8 years; range, 10-13 years). Followups were done in person, with all images and followup clinic notes. Based on the power analysis, we estimated a sample size of 178 hips was needed in each group to detect a 3-point difference in the Harris hip score with 80% power. Results At the latest followup, there were no differences between the two groups regarding the mean Harris hip scores (94 versus 94 points; p = 0.189), mean WOMAC scores (17 versus 16 points; p = 0.191), or mean UCLA activity scores (9 versus 9 points; p = 0.381). Two patients in the ultrashort stem group and one patient in the conventional stem group had severe (9 points) thigh pain, and

“…Thigh pain is known to be related to stem design and implant stiffness [5,7,14]. The normal modulus of elasticity of cortical bone is less than 20 GPa [7], whereas most conventional metal implants occupying the diaphysis have a modulus of elasticity between 80 and 200 GPa [33,40]; therefore, a short, tapered, polished intramedullary stem is one way to preserve femoral elasticity and avoid symptoms in this region. [41] after THA using tapered cementless femoral stem.…”

Section: Discussionmentioning

confidence: 99%

Long-term Results and Bone Remodeling After THA With a Short, Metaphyseal-fitting Anatomic Cementless Stem

Park

Clinical Orthopaedics &Amp; Related Research

et al. 2014

Background Long-term results of standard total hip arthroplasty (THA) in young patients were not optimal. There are a number of reported disadvantages to longer cementless stems in THA including thigh pain and proximal stress shielding. However, it is unknown whether a short, metaphyseal-fitting anatomic stem without diaphyseal fixation, which represents a possible alternative, will maintain fixation over the longer term. Question/purposes We therefore evaluated long-term (1) clinical results using validated scoring instruments; (2) osseointegration and bone remodeling; (3) complications; and (4) rates of revision and osteolysis in patients younger than 65 years who underwent THA with a short, metaphyseal-fitting anatomic cementless stem.Methods We reviewed 500 patients (630 hips) younger than 65 years (mean age at surgery, 52.7 years) who underwent THA with the Immediate Postoperative Stability stem (IPS; DePuy, Leeds, UK) by one surgeon (Y-HK) from January 1995 to March 2002. Demographic data, Harris hip score, WOMAC score, UCLA activity score, and radiographic data were recorded. All patients underwent dual-energy x-ray absorptiometry scanning of the acetabulum and proximal femur at 2 weeks after the operation and at final followup to determine stress shielding. Thigh pain was specifically investigated and scored by patients on a visual analog scale. Other complications were recorded. We determined component survival rates at 15 years using revision and aseptic loosening as end points. Minimum followup was 11 years (mean, 15.8 years; range, 11-18 years). Results The clinical and functional results improved significantly for the Harris hip score, WOMAC, and UCLA activity scores (p \ 0.001). At latest followup, mean Harris hip, WOMAC, and UCLA activity scores were 94 (range, 71-100), 15 (range, 5-29), and 7.9 (range, 6-9) points, respectively. All hips had osseous integration of the acetabular and femoral components. No patients had thigh pain. Four hips (0.6%) had deep infection and four (0.6%) had a recurrent dislocation. No patients had Grade 3 stress shielding. Fifteen-year survival rates were 98.7% (95% confidence interval [CI], 0.95-1.00) for the acetabular component and 99.4% (95% CI, 0.97-1.00) for the femoral component with revision as the end point and 100% (95% CI, 0.98-1.00) for both components with aseptic loosening as the end point. Conclusions The short, metaphyseal-fitting anatomic cementless femoral stem provided stable fixation without relying on diaphyseal fixation in younger patients, suggesting metaphyseal fitting alone is sufficient in young