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BACKGROUND: Particularly in broach-only uncemented total hip arthroplasty, a narrow femoral canal presents a technical challenge. Traditionally such femurs have been considered to be Dorr A. To our knowledge, however, no study has reported on the relationship between isthmus width and the Dorr classification. METHODS: We reviewed 500 high-quality, hard copy radiographs. Dorr classification and isthmus canal width were measured using an electronic caliper by 5 independent observers with intraobserver and interobserver error calculated. For this study, we defined a narrow canal as being ≤10 mm at its narrowest point (isthmus). RESULTS: Eight percent (40) were Dorr A, 85% (424) Dorr B, and 7% (36) Dorr C. With respect to isthmus width for Dorr A, 63% (25) were ≤10 mm compared to just 13% (55) of Dorr B. However, overall because there were more Dorr B femurs, 69% of those with an isthmus of ≤10 mm were Dorr B. CONCLUSION: In this population, almost 70% of patients with an isthmus ≤10 mm were Dorr B, with only 30% being Dorr A. When using a broach-only technique, isthmus width should be routinely measured on the preoperative anteroposterior radiographs so as to alert the surgeon to potential problems.

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There remains confusion in the literature with regard to the spinopelvic relationship, and its contribution to ideal acetabular component position. Critical assessment of the literature has been limited by use of conflicting terminology and definitions of new concepts that further confuse the topic. In 2017, the concept of a Hip-Spine Workgroup was created with the first meeting held at the American Academy of Orthopedic Surgeons Annual Meeting in 2018. The goal of this workgroup was to first help standardize terminology across the literature so that as a topic, multiple groups could produce literature that is immediately understandable and applicable. This consensus review from the Hip-Spine Workgroup aims to simplify the spinopelvic relationship, offer hip surgeons a concise summary of available literature, and select common terminology approved by both hip surgeons and spine surgeons for future research. Cite this article: Bone Joint J 2019;101-B:808-816.

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AIMS: Posterior tilt of the pelvis with sitting provides biological acetabular opening. Our goal was to study the post-operative interaction of skeletal mobility and sagittal acetabular component position. MATERIALS AND METHODS: This was a radiographic study of 160 hips (151 patients) who prospectively had lateral spinopelvic hip radiographs for skeletal and implant measurements. Intra-operative acetabular component position was determined according to the pre-operative spinal mobility. Sagittal implant measurements of ante-inclination and sacral acetabular angle were used as surrogate measurements for the risk of impingement, and intra-operative acetabular component angles were compared with these. RESULTS: Post-operatively, ante-inclination and sacral acetabular angles were within normal range in 133 hips (83.1%). A total of seven hips (4.4%) had pathological imbalance and were biologically or surgically fused hips. In all, 23 of 24 hips had pre-operative dangerous spinal imbalance corrected. CONCLUSIONS: In all, 145 of 160 hips (90%) were considered safe from impingement. Patients with highest risk are those with biological or surgical spinal fusion; patients with dangerous spinal imbalance can be safe with correct acetabular component position. The clinical relevance of the study is that it correlates acetabular component position to spinal pelvic mobility which provides guidelines for total hip arthroplasty. Cite this article: Bone Joint J 2017;99-B(1 Supple A):37-45.

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Total joint replacement patients today are younger, heavier, and more active than total joint replacement patients 40 yrs ago. Consequently, patient expectations and prosthesis requirements have increased and there is a need to re-evaluate preclinical testing methods. We present the design rationale for a novel load simulator for the proximal femur, capable of applying a more aggressive load profile than previous simulators. This simulator was used to measure three-dimensional micromotion of a cemented total hip replacement femoral stem under simulated physiological loading. We assessed the influence of a separate abductor muscle force, a higher joint reaction force, and a more accurate implant stability measurement system included in the new simulator and compared the results to the lower, single joint reaction force included in a previously published simulator. Per-cycle motion at both cement interfaces and stem and cement mantle migration obtained from both simulators using the same femoral stem design, are compared. Although the new simulator applied higher loads, per-cycle motions were lower than previously reported. In both studies, regardless of the presence or lack of a separate muscle force, the greatest motions were in the medial-lateral direction (new: 27 +/- 4 mum, old: 67 +/- 21 mum). The findings indicate that magnitude and direction of peak joint reaction force and inclusion of a separate muscle force have a significant effect on femoral stem stability measurements. We recommend that future femoral stem stability studies consider using load simulation techniques and a direct motion measurement system comparable to the one presented in this study.

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Stress shielding and load transfer to the femur following total hip arthroplasty have been studied extensively. A number of models have addressed the effects of surface finish of double-tapered, non-collared cemented stems on load transfer to the femur. However, a great number of cemented femoral stem designs in wide use today are not double tapered, and many, such as the Charnley, have collars. The effects of surface finish of such stems on load transfer to the femur are not completely understood. In this study, we measured the effects of surface finish of a straight, non-tapered cemented femoral stem, with and without a collar, in two stem sizes, on load transfer to the femur, using an in vitro laboratory model. Eight types of straight stems were fabricated, with polished or rough surfaces, with and without a collar, and in two sizes. All stems were based on the same template, and varied only in the desired combination of parameters studied. Three each of the eight unique stem types (total of 24 specimens) were cyclically loaded for 77,000 cycles at 1 Hz, alternating between walking and stair-climbing load profiles. Surface strains were measured at ten locations in each femur during designated initial and final periods. Of the three design variables, stem surface finish had the greatest effect on femoral surface strains. Specifically, compared to rough stems, with polished stems, mean proximal medial compressive strains were smaller, whereas mean distal medial compressive strains were greater. In contrast, on the anterior surface, mean proximal anterior tensile strains were greater, whereas mean distal anterior strains were smaller. All femoral surface strains increased with cyclic loading, however, strains increased at a greater rate with polished stems than with rough stems. Proximal medial strains were somewhat increased with the presence of a collar, however, these differences were small (< 100 microå ) and/or not statistically significant. Similarly, distal medial strains were increased with the presence of a collar but, again, the differences were not consistent (p > 0.16). Compared to large stems, with small stems, proximal medial compressive strains were greater. The results emphasize the importance cemented femoral stem surface roughness and the manner in which this changes stem-cement bond strength, affecting the distribution of stresses in the femur. This is an important consideration in the design of femoral stems. (Journal of Applied Biomaterials & Biomechanics 2003; 1: 76-83).

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Sixty-four hips in 62 patients were revised with a Mueller ring (28 hips), Ganz ring (18 hips), and Burch-Schneider cage (18 hips) under the direction of a single surgeon. A polyethylene cup was cemented into the metal support of all hips. Average follow-up was 4.6 years (range, 2.0-6.7 years). Six rings were revised because of aseptic loosening, and 5 others were radiographically loose, for a mechanical failure rate of 11 of 64 (17%). Acetabular metal ring supports failed by migration when defects of > or =60% of the superior weight-bearing bone were filled by only cement or particulate graft. At the time of surgery, the superior rim of the metal support should be against host-bone for 60% of its support, and if not, the use of bulk allograft, rather than particulate graft, is required. Dislocation was the second failure mechanism identified, and this occurred in 15 hips (23%), with reoperation required in 5 hips (8%). A constrained liner should be used in patients with nonunion of the trochanter and preoperative abductor weakness that grades fair/minus or worse as measured by the side-lying abduction test.

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BACKGROUND: The radiographic criteria for identification of loose cementless acetabular components have not been well established. The purpose of this study was to compare the radiographic appearance of a hemispheric porous-coated cementless cup fixed with screws with the intraoperative findings with regard to the fixation status. METHODS: The quality of the cup fixation was evaluated at fifty-two hip revisions that were performed, for reasons other than infection, at an average of 89.9 months (range, 33.8 to 150.1 months) after the primary operations. The fixation status at the revision surgery was compared with the findings on sequential anteroposterior and lateral radiographs of these sockets. Sequential radiographs of an additional 100 total hip replacements that had not required a reoperation and that had been followed for an average of 121 months were also measured. RESULTS: Loosening of the socket was radiographically identified by (1) radiolucent lines that initially appeared after two years, (2) progression of radiolucent lines after two years, (3) radiolucent lines in all three zones, (4) radiolucent lines 2 mm or wider in any zone, or (5) migration. The sensitivity of these criteria was 94%, and the specificity was 100%. The criteria had a positive predictive value of 100% and a negative predictive value of 97%. CONCLUSIONS: The most predictive radiographic findings for early diagnosis of loosening of a hemispheric porous-coated cup were progression of radiolucent lines more than two years after the operation and any new radiolucent line of 1 mm or wider that appeared more than two years postoperatively. Sequential anteroposterior and lateral radiographs are necessary to assess the time of onset and progression of radiolucent lines in order to identify loose hemispheric porous-coated cups accurately.

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Forty-eight matched pairs of osteoarthritic knees from patients who underwent primary total knee arthroplasty with a round-on-round, Apollo Knee System were studied to evaluate the outcome between all-polyethylene and metal-backed tibial components. Patients were matched for patient factors, preoperative deformities, cruciate salvage or sacrifice, and surgical technique. At the last follow-up (average, 38.4 months), there was no statistically significant difference in terms of knee scores, patient self-assessment, and radiographic outcomes. No component required revision, and no revisions were pending. Maintenance of these results over time would project into better long-term success for all-polyethylene tibial components because of the amount of wear and osteolysis with current modular metal-backed tibial components. We advocate the use of a more cost-effective all-polyethylene tibial component in elderly patients (>70 years old) who are not likely to need the versatility of exchange of a modular polyethylene insert because of wear.

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Control of the unstable THA can be problematic, but conservative management with casting and bracing can assist the patient in gaining stability, both externally and internally. The application of such appliances does not negatively affect the ultimate function of the hip and can prevent further surgical intervention.

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In summary, if TKRs are to be performed in patients who are younger and more active than those who had the initial procedures in the 1970s and 1980s, better wear performance is imperative for long-term durability, especially if surgeons continue to consider the versatility associated with modular knee-replacement systems to be a necessity. At least with some designs, including the Oxford knee and the LCS knee, the results after a minimum follow-up of 10 years are comparable with the best results after arthroplasty with fixed-bearing designs in terms of wear, loosening, and osteolysis (Table 7). As with fixed-bearing designs, there are additional challenges in terms of optimizing bearing-surface conformity and improving kinematics. Improvements in future designs of mobile-bearing total knee replacements should include better control of bearing mobility patterns to reduce the prevalence of the abnormal kinematic motions that have been observed in fluoroscopic evaluations.

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A matched pair comparison of two groups of 42 patients who had a total hip arthroplasty with uncemented fixation of the femoral stem with proximal porous coating and distal grit blasting were compared with a stem of identical design except with diaphyseal smooth surfaces. Radiographic analysis was done to determine differences in fixation and bone remodeling at the 2-year followup, and these results were compared with clinical results. The method used for measuring cortical thickness was semiquantitative, with measurements done at 15 1-cm increments beginning at 3 cm distal to the midlesser trochanter. This study determined whether, with an identical stem design, diaphyseal biologic fixation, rather than mechanical fixation, would provide better fixation without significant stress shielding differences. Seven percent of grit blasted stems had radiolucent lines in Gruen Zones 3 to 5, compared with 79% of smooth stems. The smooth stem was on average one size larger so the stress shielding was not different between matched pairs. There was a distinct pattern of adaptive remodeling that occurred in the femur with both stem surfaces. Bone loss was greatest in the proximal medial and proximal posterior bone and occurred along the entire anterior cortex. Bone thickening occurred in the distal medial and posterior cortices and extended below the tip of the prosthesis.

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Acetabular bone structure is not the same in all patients and can be defined by the radiolucent triangle superior to the acetabulum. Of 132 hips, 81 had an isosceles triangular shape, which was named type A acetabulum. Forty-six hips had an extension of the triangle into the teardrop, which created a thickened medial wall and was named type B. Five hips had a right-angle triangle, which was found only with congenital disease of the hip and was named type C. The density of the superior acetabular bone in the triangle could be normally radiolucent (stage I), have vertical and transverse trabeculae throughout the triangle (stage II), or have the triangle filled with bone and cysts (stage III). The relationship between progressive radiolucent lines and acetabular type showed that type A3 (thin medial wall with dense triangle bone) had the highest incidence of progressive radiolucent lines (P < .05).

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This study evaluated the effect of a grit-blasted diaphyseal surface on noncemented fixation of the Anatomic Porous Replacement II stem (APR-II, Sulzer Medica Orthopaedics, Austin, TX) for improvement of clinical results and fixation. A total of 107 consecutive total hip arthroplasties with the APR-II stem, which has proximal porous coating and a diaphyseal grit-blasted surface, were performed without cement, and 99 were studied at average 4 years. Of these hips, 37 had hydroxyapatite sprayed onto the proximal porous coating, but because there were no statistical differences for performance in any category, all stems were considered as 1 group. Clinical results were measured by the Harris hip score. Radiographic measurements of fixation, osteolysis, and bone remodeling were studied by reference to Gruen zones. Of hips, 99% had a good or excellent result by Harris hip score, with an average pain score of 42.3. Of hips, 98% had >40 points, with no patient reporting thigh pain after 3 years. There were no radiolucent lines in 94% of stems, and 100% had proximal bone ingrowth fixation. Distal cortical hypertrophy associated with tip fixation occurred in 49%, whereas proximal stress shielding was present in 43% of hips. Comparison of these clinical and radiographic results with our previous experience of bone ingrowth implants (smooth stem) suggests that bone ingrowth proximally with ongrowth in the diaphysis of the femoral stem provides better clinical and radiographic results.

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Thirty-eight matched pairs of osteoarthritic knees from patients who underwent primary total knee replacements with minimum 2 years of followup were studied to compare the functional outcome between a cruciate retention and posterior stabilized design with essentially identical articulation surfaces. Patients were matched for age, weight, gender, diagnosis, activity, deformity of the knee, type of tibial component, and duration of followup. The patients were evaluated functionally by three methods: the Knee Society scoring system; a self-administered questionnaire; and an activity rating based on distance walked. In addition, in vivo fluoroscopic examination was performed in 10 cruciate retention and 10 posterior stabilized knees to determine the functional knee kinematics. Results showed that by patient self-assessment, functional improvement was achieved in 35 (92%) cruciate retention knees and 36 (95%) posterior stabilized knees. There was no statistically significant difference between the two groups in the clinical evaluations. Fluoroscopic kinematics showed that the posterior stabilized knee experienced anteroposterior femorotibial translation more similar to the normal knee during normal gait and deep knee bend. These clinically equivalent results are not in agreement with the predicted better functional results of cruciate retained knees as determined by gait studies.

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BACKGROUND: Total hip replacements with a metal-on-metal articulation were commonly used until the mid-1970s; most were then abandoned in favor of hip replacement with a metal-on-polyethylene articulation. The reason for this change was primarily early cup loosening, which was more prevalent with these metal-on-metal designs than it was with metal-on-polyethylene designs. In the late 1980s, a metal-on-metal design with improved clearance (adequate space between the femoral head and the acetabular articulation surface to allow fluid film lubrication and clearance of any debris from within this joint), metal hardness, and reproducible surfaces was introduced by Sulzer Orthopedics in Switzerland. Orthopaedic surgeons were interested in this Metasul articulation because the contribution of polyethylene wear particles to the failure of total hip replacements had become evident. This study was undertaken to review the clinical performance of this implant and to determine if early acetabular loosening or revision and wear and osteolysis were prevalent. METHODS: Between 1991 and 1994, seventy patients (seventy hips) had a total hip replacement with the Metasul metal-on-metal articulation and a cemented Weber cup. Nine patients died less than four years after the replacement; none of these deaths were related to the operation. Five patients were not available for radiographic evaluation, but they were contacted and it was known that the hip was not painful and had not been revised. Fifty-six patients (fifty-six hips) had complete clinical and radiographic data four to 6.8 years after the operation, and they made up the study group. The patients were evaluated with use of the Harris hip score, a patient-self-assessment form, and radiographs. RESULTS: At an average of 5.2 years (range, four to 6.8 years) after the operation, the average total Harris hip score for the fifty-three patients who did not have a revision was 89.6 points (range, 62 to 100 points). The average Harris pain score was 41.0 points (range, 30 to 44 points), and the average Harris limp score was 9.4 points (range, 5 to 11 points). One patient had revision of a loose cup, but there were no other loose acetabular components in the series. Two patients had revision of the acetabular component because of dislocation. No patient had a loose or revised femoral component. Therefore, the mechanical failure rate was one (2 percent) of fifty-six patients. Thirty-six of forty-seven patients who completed the patient-self-assessment form rated their result as excellent; seven, as very good; two, as good; one, as fair; and one, as poor. Wear could not be measured on radiographs because of the metal-on-metal articulation. No hip had radiographic evidence of acetabular osteolysis and two hips had calcar resorption, but there was no other radiographic evidence of focal osteolysis. CONCLUSIONS: Our four to seven-year experience with this articulation surface indicates that the clinical results are similar to those of total hip replacements with a metal-on-polyethylene articulation. We believe that the Metasul articulation may have a role in reducing the wear that occurs with total hip replacement. The Metasul articulation appears to be particularly indicated for more active patients. A historical comparison with the reports in the literature of which we are aware indicated that the hips in our study had a lower rate of acetabular revision and loosening than did those with previous metal-on-metal designs and that they had no more acetabular loosening or osteolysis than did those with metal-on-polyethylene articulations followed for an average of five years.

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Highly cross-linked polyethylenes represent a new class of polyethylenes that demonstrate dramatic improvements of wear characteristics in laboratory tests. Cross-linked polyethylenes can be manufactured by a number of methods, all of which lead to some changes in the physical properties of the polyethylene. The very limited clinical information about cross-linked polyethylenes available has been favorable. Cross-linked polyethylenes appear to hold promise as an alternative to conventional polyethylene and to hard-on-hard bearing surfaces, but much more clinical information will be required before they can be recommended for routine clinical use.

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