The acetabular labrum is a soft-tissue structure which lines the acetabular rim of the hip joint. Its role in hip joint biomechanics and joint health has been of particular interest over the past decade. In normal hip joint biomechanics, the labrum is crucial in retaining a layer of pressurised intra-articular fluid for joint lubrication and load support/distribution. Its seal around the femoral head is further regarded as a contributing to hip stability through its suction effect. The labrum itself is also important in increasing contact area thereby reducing contact stress. Given the labrum’s role in normal hip joint biomechanics, surgical techniques for managing labral damage are continuously evolving as our understanding of its anatomy and function continue to progress. The current paper aims to review the anatomy and biomechanical function of the labrum and how they are affected by differing surgical techniques.

Take home message: The acetabular labrum plays a critical role in hip function and maintaining and restoring its function during surgical intervention remain an essential goal.

Cite this article: Bone Joint J 2016;98-B:730–5.

Summary

The cartilage layer from cam-type femoroacetabular impingement deformities had lower stiffness and increased permeability compared to normal cartilage. This is consistent with osteoarthritis and supports the hypothesis of abnormal contact stresses.

Impaction allografting is increasingly used for the treatment of failed total hip replacements. In six human cadaveric femurs the impaction allografting procedure was performed to comprehensively describe the postoperative morphology of impaction allografting. After the procedure, the specimens were sectioned and prepared for histomorphometric analysis. The graft porosity was lowest in Gruen zone four (52%) and highest in Gruen zone one (76%). At the level of Gruen zone six and two, virtually the entire cross-section was filled with bone cement. The presented data will serve as a baseline for future investigations of the impaction allografting.

Impaction allografting is an attractive procedure for the treatment of failed total hip replacements. The purpose of this study was to comprehensively describe the morphology of impaction allografting post operatively to form a baseline for further investigations.

Three experienced surgeons performed the impaction allografting procedure on six cadaveric femurs. After the procedure, the femurs were cut in 6mm thick transverse sections and processed for histomorphometric analysis.

The porosity of the impacted graft was highest proximally in Gruen zone one (76%) and lowest in Gruen zone four (52%). Below the tip of the stem (Gruen zone four), the mean cement penetration was significantly lower compared to the proximal part of the femur. The averaged residual impacted graft layer in Gruen zone six and two was (0.5mm SD 0.4mm) significantly thinner compared with Gruen zone’s one, 7/1, and four.

In the region of Gruen zone six and two the entire cross-section was penetrated with bone cement with almost no residual graft layer (Figure). Even the simulated lytic defects in this region were filled with the graft cement composite which may not be remodelled by the host bone.

The graft porosity was found to be highest proximally and lowest distally. In the region of Gruen zone six and two the entire cross-section was penetrated with bone cement with almost no residual graft layer.

This investigation will serve as a baseline for future studies of the mechanical and biological processes that make the impaction allografting a successful procedure.

Funding: Stryker Howmedica and DePuy for provided implants and instruments.

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In impaction allografting, the host bone interface consists of morsellized allograft alone or as a composite with bone cement. The objective of this study was to investigate the host bone temporal changes in the interface for these two materials in a rat bone chamber model. The composite-host bone interface strength was significantly higher at three weeks and was higher than the allograft construct. Limited allograft, but extensive periosteal remodelling, was observed at three weeks. At six weeks a new medullary canal was formed and the endosteal cortex was partially absorbed. Endosteal absorption resulting in medullary canal widening may be responsible for clinically unstable stems after impaction allografting.

The host bone interface after impaction allografting consists of morsellized allograft alone or as a composite with cement and it may be important for the clinical success of this procedure. The purpose of this study was to investigate the temporal changes of these interfaces in a rat bone chamber model.

Bone chambers were inserted in both tibiae of thirty-three rats and tightened to the endosteal surface to create a microenvironment. One chamber was filled with allograft bone and the other with an allograft/ cement composite. After zero, three, and six weeks, the rats were euthanized, the interfaces mechanically tested and processed for histomorphometric analysis.

The composite-host bone interface strength was significantly higher at three weeks and was higher than the allograft construct. Extensive periosteal remodelling was observed at three weeks. At six weeks a new medullary canal was formed and the endosteal cortex was partially absorbed.

The increased interface strength of the composite-host bone interface was due to fibrous tissue attachment rather than direct bonding of the bone particles. Cortical porosity and cancellisation is known to be caused by a damaged endosteal circulation resulting in medullary canal widening and may cause clinically unstable implants.

Interface strength of the composite-host bone interface was increased at three weeks through fibrous tissue attachment. A damaged endosteal circulation caused cortical porosis and cancellisation.

With this rat bone chamber model a potential cause of stem subsidence after impacting allografting was identified.

Funding: The George W. Bagby Research Fund.

The Canadian Institutse of Health Research.

The Maurice E. Müller Foundation.

The Swiss Academy of Engineering Science.

The Robert Mathys Foundation.

Purpose: In-vitro mechanical tests are often used to pre-clinically assess the primary stability of hip endopros-theses. There is no standard protocol for these tests and the test conditions used vary greatly. This study examined the effect of the abductor muscle and the anterior-posterior component of the hip contact force (Fap) on the primary stability of cementless stems.

Methods: Cementless stems were implanted in 12 composite femurs which were divided into two groups: group 1 (N=6) was loaded with the hip contact force only, whereas group 2 (N=6) was additionally subjected to an abductor force. The cranial-caudal component of the hip contact force was the same in both groups, i.e. 2.3BW at 13° from the femur long axis. Each specimen was subjected to three Fap levels: 0, 0.3BW (walking), and 0.6BW (stair climbing). The implant translation relative to the femur was measured using a custom-built system comprised of 6 LVDT sensors. The resultant migration and micromotion were analyzed using an ANOVA with the abductor a between-group factor and Fap a within-group factor, followed by SNK post-hoc analysis with a significance level of 95%.

Results: Implant motion was not significantly affected when the Fap was increased from 0 to 0.3BW. However, without abductor, increasing Fap from 0.3 to 0.6BW increased migration and micromotion by an average of 291& #956;m (285% increase), and 15& #956;m (75%) respectively. With abductor, increasing Fap to 0.6BW increased migration by 87& #956;m (79%) but did not affect micromotion. The abductor did not significantly affect stem motion at lower Fap, but at Fap = 0.6BW motion was 50% lower compared with hip contact forces only.

Conclusions: Based on these results, inclusion of either abductor and/or Fap has little effect on implant motion when simulating walking. However, stair climbing (higher Fap) generates greater bone-implant motion compared to walking loads, and this effect is greatest in the absence of an abductor force. Funding: Other Education Grant Funding Parties: The Michael Smith Foundation for Health Research

This study explored the relationship between the initial stability of the femoral component and penetration of cement into the graft bed following impaction allografting.

Impaction allografting was carried out in human cadaveric femurs. In one group the cement was pressurised conventionally but in the other it was not pressurised. Migration and micromotion of the implant were measured under simulated walking loads. The specimens were then cross-sectioned and penetration of the cement measured.

Around the distal half of the implant we found approximately 70% and 40% of contact of the cement with the endosteum in the pressure and no-pressure groups, respectively. The distal migration/micromotion, and valgus/varus migration were significantly higher in the no-pressure group than in that subjected to pressure. These motion components correlated negatively with the mean area of cement and its contact with the endosteum.

The presence of cement at the endosteum appears to play an important role in the initial stability of the implant following impaction allografting.

We studied various aspects of graft impaction and penetration of cement in an experimental model. Cancellous bone was removed proximally and local diaphyseal lytic defects were simulated in six human cadaver femora. After impaction grafting the specimens were sectioned and prepared for histomorphometric analysis.

The porosity of the graft was lowest in Gruen zone 4 (52%) and highest in Gruen zone 1 (76%). At the levels of Gruen zones 6 and 2 the entire cross-section was almost filled with cement. Cement sometimes reached the endosteal surface in other Gruen zones. The mean peak impaction forces exerted with the impactors were negatively correlated with the porosity of the graft.