Aim

Our collaborative study aims to demonstrate that acute partial Achilles Tendon Tears (ATTs) are not separate diagnostic entities from full ATTs. and should be thought of as a continuum rather than binary partial or full.

Objectives

The Precice nail is the latest intramedullary lengthening nail with excellent early outcomes. Implant complications have led to modification of the nail design. The aim of this study was to perform a retrieval study of Precice nails following lower-limb lengthening and to assess macroscopical and microscopical changes to the implants and evaluate differences following design modification, with the aim of identifying potential surgical, implant, and patient risk factors.

Aims

The management of a significant bony defect following excision of a diaphyseal atrophic femoral nonunion remains a challenge. We present the outcomes using a combined technique of acute femoral shortening, stabilized with a long retrograde intramedullary nail, accompanied by bifocal osteotomy compression and distraction osteogenesis with a temporary monolateral fixator.

Introduction

The Precice nail is the latest intramedullary lengthening nail with excellent early outcomes. Implant complications have led to modification of the nail design. The aim of this study was to perform a retrieval study of Precice nails following lower limb lengthening. To assess macroscopic and microscopic changes to the implants and assess differences following design modification, with identification of potential surgical, implant and patient risk factors.

Introduction

The management of a significant bone defect following excision of a diaphyseal atrophic femoral non-union remains a challenge. Traditional bone transport techniques require prolonged use of an external fixator with associated complications. We present our clinical outcomes using a combined technique of acute femoral shortening, stabilised with a deliberately long retrograde intramedullary nail, accompanied by bifocal osteotomy compression and distraction osteogenesis to restore segment length utilising a temporary monolateral fixator.

Metal on Metal hip resurfacing (MoM HR) can be an effective operation for the young arthritic hip population. However, errors in cup orientation have been associated with increased wear, circulating blood metal ions, and soft tissue abnormalities that can lead to premature failure of the bearing surface and subsequent revision surgery. While image free computer guidance has been shown to increase surgical accuracy in total hip arthroplasty, the role of image based technology in MoM HR is unclear. In this study, we compared the accuracy of cup orientation in MoM HR performed by either freehand technique or CT based navigation.

Seventy five patients (81 hips) underwent either freehand (n=42) or navigation (n=39) surgery, both requiring a three dimensional (3D) CT surgical plan. Surgery was conducted by hip specialists blind to the method of cup implantation until the operation. Deviation in inclination and version from the planned orientation, as well as, number of cups within a 10° safe zone and 5° optimal zone of the target position was calculated using post operative 3D CT analysis.

Error in inclination was significantly reduced with navigation compared to freehand technique (4° vs 6°, p=0.02). We could not detect a difference between the two groups for version error (5° vs 7°, p=0.06). There was a significantly greater number of hips within a 10° (87% vs 67%, p=0.04) and 5° (50% vs 20%, p=0.06) safe zone when navigated.

Image based navigation can substantially improve accuracy in cup orientation. The results of our freehand group appear better than historic controls, suggesting the use of a 3D plan may help to reduce technical error and improve the learning curve in this technically demanding procedure. We advocate the use of image based navigation in MoM hip resurfacing arthroplasty.

The radiographic analysis of over 5000 metal on metal (MoM) hips using Ein Bild Roentgen Analyse (EBRA) software have been recently published in an attempt to determine the influence of cup orientation on bearing function. The validation of this software relies one study, conducted in a phantom pelvis without a femoral head in situ. Three dimensional computed tomographic (3D-CT) has been shown to be more accurate for hip and knee arthroplasty than plain radiographs for measurements of component orientation and position. The accuracy of EBRA when compared to 3D-CT for MoM hips specifically is unclear.

We measured the cup orientation of 96 large diameter MoM hips using EBRA analysis of plain radiographs and compared this to 3D-CT. All measurements were made using the radiographic definition of cup orientation. The mean difference in version between the two imaging modalities was 8°; with wide limits of agreement of −21.2° and +5.6°. Three retroverted cups were not detected by EBRA. The mean difference in inclination values was 0.3°, but there was up to 9°difference between imaging modalities. When measured by 3D CT, 64% of hips were within a 10° safe zone around 45° inclination and 20° version, compared to only 24% when measured by EBRA (Fishers Exact test, p< 0.0001).

The measurement of cup orientation of MoM hips using EBRA software is insufficiently accurate, particularly for the assessment of cup version. The cup rim is obscured by the large diameter femoral head on plain radiographs. Research studies using EBRA analysis for version have limited value if accuracy of more than 20 degrees is required to draw conclusions. This software may not be suitable to measure the performance of a device or surgeon. The limitations of EBRA can be overcome, if 3D-CT with an extended Hounsfield scale for data capture is used.

Introduction: Local problems of metal on metal (MOM) hip arthroplasty such as pseudotumours, neck thinning and osteolysis maybe related to concentrations of cobalt and chromium ions in the synovial fluid. There is little reported on these values. Our aim was to determine the range of metal ion levels in synovial fluid, and to investigate the relationship between these samples and simultaneous blood samples.

Methods: Synovial fluid and whole blood samples were taken from 30 consecutive patients at the time of revision surgery for a painful MOM hip. Aspirated fluid was not visibly contaminated with blood. Impants were in situ for a mean period of 31 months. All had normal renal function. Samples were analysed using ICP mass spectrometry and compared with 10 samples from patients without implants.

Results: The mean (and range) of synovial fluid metal ion levels were 1965 ug/l (30 to 13618) and 6265 ug/l (11 to 81630) for Cobalt and Chromium respectively. There was a good correlation between synovial and blood levels for both cobalt (R=0.65, p = 0.0001) and chromium (R = 0.59, p = 0.006).

Discussion and Conclusion: Metal ions in synovial fluid from MOM hips are generated from wear of the bearing surfaces, the correlation with blood metal ion levels, shown in this study, suggest that blood levels may be used as surrogate marker for hip wear rate. Our range of synovial fluid metal ion levels may be useful for those conducting in vitro studies on the biocompatibility of MOM hips.

A robust frame of reference is required to accurately characterize pathoanatomy in the proximal femur and quantify the femoral head-neck relationship. A three dimensional (3D) femoral neck axis (FNA) could serve such a purpose, but has not yet been established in the current literature.

The primary aim of this study was to develop and evaluate a reliable method of determining the 3D femoral neck axis. Secondly, we wanted to quantify the translational relationship between the femoral head and neck in normal and cam type hips.

Pelvic computed tomographic scans (CT) and radiographs were retrieved from our database of patients who had undergone navigated hip surgery or CT colonography. All patients had given informed consent for their medical files and imaging to be used for research purposes, as approved by the institutional review board.

Pre-operative scans were performed using the Siemens Sensation 64 slice scanner (Siemens Medical Solutions, Erlangen, Germany). The Imperial Protocol developed at the authors’ orthopaedic unit was applied, allowing acquisition of Digital Imaging and Communications in Medicine (DICOM) files of 0.75mm thickness.

Normal and cam type hips (n=30) were identified for analysis. ‘Normal’ hips (n=15) were defined in asymptomatic patients with no previous history of hip disease, and, no obvious abnormality on radiographs or CT. The ‘cam’ hip type (n=15) was defined by the presence of an anterior osseous bump at the head-neck junction, and an alpha angle greater than 50° on hip radiographs.

DICOMs were converted to 3D stereolith (STL) images using validated commercial image processing and analysis software (3-Matics, Materialise Group, Leuven, Belgium).

In order to determine the 3D-FNA, a best fit sphere was applied to the femoral head with a root mean square error of less than 0.5mm. The border between sphere and femoral neck defined the head -neck junction. The bone surface was marked here (including the anterior bump in cam hips) and at the neck base, providing two anatomical rings that defined the superior and inferior limits of the femoral neck. The centre point of each ring was calculated. A line connecting these points defined the femoral neck axis, and was verified on a DICOM viewer in sagittal, axial and coronal planes. The offset between the femoral head centre and neck axis was measured.

The 3D image and axis were further analysed to examine the femoral head-neck relationship, using customized software developed at our institution and previously validated in previous research projects.

To standardize rotational alignment, the femoral neck was aligned vertically in two planes by creating an axis between the tip of the greater trochanter and the center of the lesser trochanter. The aligned proximal femur was viewed end on, and the version of the head relative to the neck determined by calculating the angle between the head centre and a vertical marker placed at the 12 o’clock position. Angles below 180° demonstrated anteversion, while those above 180° demonstrated retroversion.

Cam femoroacetabular impingement (FAI) is currently treated by resecting the femoral cam lesion. Some surgeons advocate additional anterosuperior acetabular rim resection. However, the exact acetabular contribution to cam-FAI has yet to be described. Using 3D-CT analysis, we set out to quantify the acetabular rim shape and orientation in this condition, and to determine the roles of these factors in cam-FAI.

The acetabula of twenty consecutive cam hips (defined by α-angle of Notzli greater than 55° on plain radiographs) undergoing image based navigated surgery. These were compared with twenty normal hips (defined as disease free sockets with a normal femoral head-neck junction) obtained from a CT colonoscopy database.

Using 3D reconstruction software, the pelvis was aligned to the anterior pelvic plane (APP). Starting at the most anterior rim point, successive markers were placed along the rim. A best-fit acetabular rim plane (ARP) was derived, and the subtended angle (SA) between each rim marker and a normal vector from the acetabular centre was calculated. Values above 90° indicated a peak, with less than 90° representing a trough. Inclination and version were measured from the APP.

Our results showed that the rim profile of both cam-type and normal acetabular is an asymmetric succession of three peaks and three troughs. However, the cam-type acetabulum is significantly shallower overall than normal (Mean SA: 84±5° versus 87±4°, p< 0.0001). In particular, at anatomical points in the impingement zone between 12 and 3 o’clock, the subtended angle of cam hips were never higher than normal, and, in fact, at certain points were lower (iliac eminence: 90±5° vs. 93±4° p=0.0094, iliopubic trough: 79±5° vs. 83±4° p=0.0169, pubic eminence 83±7° vs. 84±4° p=0.4445). The orientation of cam and normal hips were almost identical (Inclination: 53±4°vs. 51±3° p=0.2609 and Anteversion: 23±7° vs. 24±6° p=0.3917).

We concluded that cam-type acetabula are significantly shallower than normal. The subtended angles at all points around the hip were lower, and in particular, in the impingement zone between 12 and 3 o’clock not one cam had a subtended angle over 90°. We have therefore been unable to support the hypothesis of mixed-type FAI in cam-type hips.

Bony rim resection in cam hips therefore runs the risk of rendering the acetabulum more morphologically abnormal and even functionally dysplastic. We do not recommend acetabular rim resection in patients with pure cam-type impingement, and await the longer-term results of this practice with apprehension.

A 10° deviation from the ideal cup orientation in Metal on Metal (MoM) bearing couples leads to increased wear and the subsequent risk of early revision surgery. We assessed the accuracy of orthopaedic trainees and consultants in achieving optimal acetabular cup orientation.

49 trainees and 18 consultants were asked to orientate an acetabular component to 40° inclination and 20° anteversion in 3 consecutive pelvic models:

osteoarthritic (OA),

The trainee group experience in performing hip arthroplasty procedures ranged from novice to expert (> 100 procedures performed). Performance was measured using an image based navigation system.

Average angular error in all tasks was less than 10°, but the range in anteversion or inclination was up to 65°. Eighteen percent of trainees were +/− 10° of the target orientation in Station A, 29% in B and 2% in C. Forty four percent of consultants achieved the safe zone in A, 16% in B and 0% in C. There was no significant difference in accuracy between the two groups in any of the tasks (p> 0.01). There was no correlation between experience and angular accuracy.

We have been unable to demonstrate trainees have the ability to achieve the optimal cup orientation in a clinically relevant safe zone. A similar range of error is found in experienced surgeons. Focused training or intra-operative computer assistance may provide the solution to improving accuracy in this core orthopaedic skill.

Pincer femoroacetabular impingement (FAI) is cited as being the result of a socket that is either too deep or retroverted, or both. Using 3D-CT analysis, we set out to quantify the acetabular rim shape and orientation to determine the roles of these two factors in FAI.

Twenty pincer acetabulae were selected from patients undergoing image based navigated surgery, where the lateral centre edge angle was greater than 40° on plain radiographs. The normal group of disease free sockets were obtained from a CT colonography database.

Using 3D reconstruction of their CT scans, a novel method of mapping the acetabular rim profile was created. The pelvis was aligned to the anterior pelvic plane. Starting at the most anterior rim point, successive markers were placed along the rim. A best fit plane (ARP) through the acetabulum was derived, and the subtended angle (SA) between each rim marker and a normal vector from the acetabular centre was calculated. Values above 90° indicated a peak, with less than 90° representing a trough. Inclination and version were measured from a horizontal plane and the ARP, in the coronal and axial view respectively.

The results showed that asymmetric acetabular rim profiles in normal and pincer hips were very similar. However, pincer hips are significantly deeper overall (Mean SA 96±5° vs. 87±4° p< 0.00001) and at each anatomical point of the three eminences (pubic [SA: Normal 84±4° vs. Pincer 94±7° p< 0.00001], iliac [SA: 93±4° vs. 100±6° p=0.00021] and ischial [SA: 92±3° vs. 102±8° p=0.00005]) and two troughs (ilio-pubic [SA: Normal 83±4° vs. Pincer 94±8° p=0.00001] and ilio-ischial [SA: 92±3° vs. 102±8° p=0.00002]).

The orientation of normal and pincer were almost identical (Inclination: 51±3° vs. 51±6° p=0.54 and Version: 24±6° vs. 25°±7° p=0.67).

We conclude that the rim shape of pincer hips follows the same contour as normal hips. In agreement with current radiographic diagnosis, pincer-type hips are characterised by a deeper acetabulum. This ‘overcoverage’ of the femoral head confirms the biomechanical model of pincer-type impingement.

Both inclination and version in these two groups were almost identical, with no truly retroverted acetabulum seen. Pincer impingement resulting from ‘acetabular retroversion’ is a concept currently based upon radiographic signs that we have been unable to confirm in this small 3D study using the subtended angle as the key descriptor of acetabular morphology.

Large-head metal-on-metal total hip replacement has a failure rate of almost 8% at five years, three times the revision rate of conventional hip replacement. Unexplained pain remains a feature of this type of arthroplasty.

All designs of the femoral component of large-head metal-on-metal total hip replacements share a unique characteristic: a subtended angle of 120° defining the proportion of a sphere that the head represents. Using MRI, we measured the contact area of the iliopsoas tendon on the femoral head in sagittal reconstruction of 20 hips of patients with symptomatic femoroacetabular impingement. We also measured the articular extent of the femoral head on 40 normal hips and ten with cam-type deformities. Finally, we performed virtual hip resurfacing on normal and cam-type hips, avoiding overhang of the metal rim inferomedially.

The articular surface of the femoral head has a subtended angle of 120° anteriorly and posteriorly, but only 100° medially. Virtual surgery in a normally shaped femoral head showed a 20° skirt of metal protruding medially where iliopsoas articulates.

The excessive extent of the large-diameter femoral components may cause iliopsoas impingement independently of the acetabular component. This may be the cause of postoperative pain with these implants.

We retrospectively analysed concentrations of chromium and cobalt ions in samples of synovial fluid and whole blood taken from a group of 92 patients with failed current-generation metal-on-metal hip replacements. We applied acid oxidative digestion to our trace metal analysis protocol, which found significantly higher levels of metal ion concentrations in blood and synovial fluid than a non-digestive method. Patients were subcategorised by mode of failure as either ‘unexplained pain’ or ‘defined causes’. Using this classification, chromium and cobalt ion levels were present over a wider range in synovial fluid and not as strongly correlated with blood ion levels as previously reported. There was no significant difference between metal ion concentrations and manufacturer of the implant, nor femoral head size below or above 50 mm. There was a moderately positive correlation between metal ion levels and acetabular component inclination angle as measured on three-dimensional CT imaging.

Our results suggest that acid digestion of samples of synovial fluid samples is necessary to determine metal ion concentrations accurately so that meaningful comparisons can be made between studies.