Oxidized Zirconium Components Maintain a Smooth Articular Surface Except Following Hip Dislocation.

BACKGROUND: Oxidized zirconium (OxZr) offers theoretical advantages in total hip and knee arthroplasty (THA and TKA, respectively) relative to other biomaterials by combining the tribological benefits of ceramics with the fracture toughness of metals. Yet, some studies have found that OxZr does not improve outcomes or wear rates relative to traditional bearing materials such as cobalt-chromium (CoCr). Separately, effacement of the thin ceramic surface layer has been reported for OxZr components, though the prevalence and sequelae are unclear. METHODS: To elucidate the in vivo behavior of OxZr implants, the articular surfaces of 94 retrieved THA and TKA femoral components (43 OxZr TKA, 21 OxZr THA, 30 CoCr THA) were analyzed using optical microscopy, non-contact profilometry, and scanning electron microscopy. RESULTS: We found that OxZr components maintain a smooth articular surface except following hip dislocation. Three of four OxZr femoral heads revised following dislocation exhibited severe damage to the articular surface, including macroscopic regions of ceramic-layer effacement and exposure of the underlying metal substrate; these components were 23-32 times rougher than pristine OxZr controls. When revised for dislocation, OxZr femoral heads were substantially rougher than CoCr femoral heads (median Sa = 0.431 v. 0.020 µm, P = .03). In contrast, CoCr femoral heads exhibited low overall roughness values regardless of whether they dislocated (median Sa = 0.020 v. 0.008 µm, P = .09, CoCr dislocators v. non-dislocators). CONCLUSIONS: Effacement of the ceramic surface layer and substantial articular surface roughening is not atypical following dislocation of OxZr femoral heads, making OxZr much less tolerant than CoCr to hip dislocation.

Flexion contracture due to cyclops lesion after bicruciate-retaining total knee arthroplasty.

Flexion contracture may develop after total knee arthroplasty (TKA) and is usually associated with soft tissue contracture in the posterior compartment or hamstrings. A cyclops lesion is a soft tissue mass which can form in the anterior compartment usually after anterior cruciate ligament reconstruction and has been observed after bicruciate-retaining TKA. We have treated a patient who developed progressive loss of full extension from 0° to 20° after bicruciate-retaining TKA. A large fibrous tissue mass (cyclops lesion) was identified in the anterior compartment during arthrotomy 1 year after TKA. Excision of the mass resulted in complete resolution of the flexion contracture.

Relationship Between Functional Anatomy of the Hip and Surgical Approaches in Total Hip Arthroplasty.

Multiple surgical approaches have been used successfully for total hip arthroplasty. Minimally invasive surgery, defined by the length of the incision, has been associated with less blood loss and shorter length of stay compared with conventional total hip arthroplasty. Differences in early functional outcomes, as well as the risk of early and long-term complications, have been observed between different anatomic surgical approaches. However, no single surgical approach has been established that achieves both the shortest functional recovery and the lowest rate of complications after total hip arthroplasty. [Orthopedics. 2019; 42(4):e356-e363.].

Novel Acetabular Cup for Revision THA Improves Hip Center of Rotation: A Radiographic Evaluation.

BACKGROUND: Bone loss in patients undergoing revision THA poses a considerable challenge for orthopaedic surgeons. Often, to achieve better fixation in remaining bone, larger diameter acetabular components and reaming superiorly may be necessary. However, this is likely to raise the hip center of rotation, which may lead to altered biomechanics, specifically, insufficiency of the abductor muscles, altered gait, and increased risk of dislocation from impingement. More recently, a newer acetabular shell has been designed to more closely replicate the native hip center of rotation in these circumstances while maintaining adequate fixation. QUESTIONS/PURPOSES: The purpose of this study was to compare the radiographic parameters of this newer design with conventional hemispheric cups in revision THA. Specifically, we assessed the differences in (1) vertical center of rotation (COR) displacement and (2) horizontal COR displacement. METHODS: Between January 2016 and April 2016, five reconstructive surgeons at five institutions utilized a newer highly porous acetabular shell designed with peripheral screw holes and vertically eccentric COR to allow for restoration of center of hip rotation in revision THA. We included all patients who received this device. During this time, the general indications at these sites for using the new device included Paprosky Stage IIA, IIB, IIC, or IIIA acetabular defects. This yielded 29 patients who were subsequently matched (one to two) by cup size and sex to a cohort who underwent revision THA with conventional hemispheric cups between January 2015 and May 2016. To determine hip COR, radiographic measurements were performed. A circle contiguous to the acetabulum was drawn and the center was determined as the hip COR. All measurements were made from the interteardrop line for both the revised and native hips. A line through the teardrops was used for all horizontal measurements. Center position adjustments were made based on the manufacturer-specified values. Comparisons were performed using chi-square tests for categorical and t-tests for continuous variables. There was no difference in the severity of bone loss before the revision in the groups, as evidenced by Paprosky staging of preoperative radiographs. RESULTS: The mean vertical COR displacement was smaller in patients who had the novel cup (3.5 mm; range, -12 to 15 mm; mean difference, -7.3 mm; 95% confidence interval [CI], -13.2 to -1.5) as compared with those who had the conventional cup (10.5 mm; range, -4 to 50 mm; mean difference, 7.3 mm; 95% CI, -12.5 to -2.2; p = 0.003). There was no difference in mean horizontal displacement between the two groups (-0.06 ± 6.1 versus 1.7 ± 7.1; mean difference, -1.8; p = 0.903). CONCLUSIONS: Although hip COR was improved based on radiographic measurements with the use of this novel acetabular design, and although this may improve hip biomechanics, more studies are required before its widespread adoption for revision cases of this nature can be recommended. Both implant costs and the risks associated with using a new design in practice will have to be justified by studies that evaluate fixation, clinical function and implant survival, and patient-reported outcome scores, all of which were beyond the scope of this preliminary report. LEVEL OF EVIDENCE: Level III, therapeutic study.

Effect of processing, sterilization and crosslinking on UHMWPE fatigue fracture and fatigue wear mechanisms in joint arthroplasty.

Ultra high molecular weight polyethylene (UHMWPE) has been used as a bearing surface in total joint replacements (TJR) for nearly five decades. This semi-crystalline polymer has extraordinary energetic toughness owing to its high molecular weight and entanglement density. However, it is challenged by a need to offer a combined resistance to fatigue, wear and oxidation in vivo. The processing, sterilization treatment, and microstructural tailoring of UHMWPE has evolved considerably in the past 50 years but an optimized microstructure remains elusive. This review seeks to provide an overview of this processing history to address two primary questions: First, how does microstructure affect fatigue fracture and fatigue wear mechanisms in UHMWPE? And second, can microstructure be optimized to provide resistance to fatigue, oxidation and wear in vivo? Previous literature demonstrates that while crosslinking improves resistance to adhesive/abrasive wear, it also reduces resistance to fatigue crack propagation and fatigue wear by restricting molecular mobility and rendering the polymer more brittle. Crystallinity improves fatigue resistance but generally increases elastic modulus and concomitant contact stresses in vivo. The presence of fusion defects or oxidation reduces further fatigue resistance and enhances fatigue wear. Thus, UHMWPE microstructural evolution comes with trade-offs. Currently there is no singular formulation of UHMWPE that is ideal for all TJR applications.

Comparison of Head Center Position and Screw Fixation Options Between a Jumbo Cup and an Offset Center of Rotation Cup in Revision Total Hip Arthroplasty: A Computer Simulation Study.

Jumbo acetabular cups are commonly used in revision total hip arthroplasty (THA). A straightforward reaming technique is used which is similar to primary THA. However, jumbo cups may also be associated with hip center elevation, limited screw fixation options, and anterior soft tissue impingement. A partially truncated hemispherical shell was designed with an offset center of rotation, thick superior rim, and beveled anterior and superior rims as an alternative to a conventional jumbo cup. A three dimensional computer simulation was used to assess head center position and safe screw trajectories. Results of this in vitro study indicate that a modified hemispherical implant geometry can reduce head center elevation while permitting favorable screw fixation trajectories into the pelvis in comparison to a conventional jumbo cup.