We examined the relationship between the size of the femoral cam in femoroacetabular impingement (FAI) and acetabular pathomorphology to establish if pincer impingement exists in patients with a femoral cam.

CT scans of 37 symptomatic impinging hips with a femoral cam were analysed in a three-dimensional study and were compared with 34 normal hips. The inclination and version of the acetabulum as well as the acetabular rim angle and the bony acetabular coverage were calculated. These measurements were correlated with the size and shape of the femoral cams.

While the size of the femoral cam varied characteristically, the acetabular morphology of the two groups was similar in terms of version (normal mean 23° (sd 7°); cam mean 22° (sd 9°)), inclination (normal mean 57° (sd 5°); cam mean 56° (sd 5°)), acetabular coverage (normal mean 41% (sd 5%); cam mean 42% (sd 4%)) and the mean acetabular rim angle (normal mean 82° (sd 5°); cam mean 83° (sd 4°)).

We found no correlation between acetabular morphology and the severity of cam lesion and no evidence of either global or focal over-coverage to support the diagnosis of ‘mixed’ FAI. The femoral cam may provoke edge loading but removal of any acetabular bearing surface when treating cam FAI might induce accelerated wear.

Cite this article: Bone Joint J 2013;95-B:314–19.

In a global environment of rising costs and limited funds, robotic and computer-assisted orthopaedic technologies could provide the means to drive a necessary revolution in arthroplasty productivity. Robots have been used to operate on humans for 20 years, but the adoption of the technology has lagged behind that of the manufacturing industry. The use of robots in surgery should enable cost savings by reducing instrumentation and inventories, and improving accuracy. Despite these benefits, the orthopaedic community has been resistant to change. If the ergonomics and economics are right, robotic technology just might transform the provision of joint replacement.

Introduction

Differing descriptions of patellar motion relative to the femur have resulted from many in-vitro and in-vivo studies. The aim of this study was to examine the tracking behaviour of the patella. We hypothesized that patellar kinematics would correlate to the trochlear geometry.

Introduction

Tibial patho-morphology has been described as a factor that predisposes to medial compartment osteoarthritis of the knee in 2D analysis. The aim of this study was to investigate whether the morphology of normal and pre-OA medial compartments are really different in 3 dimensions.

Introduction

SPECT/CT might be a promising diagnostic modality in patients with painful total knee arthroplasty. It was the purpose of our study to introduce a novel standardised SPECT/CT algorithm for assessing patients with painful primary total knee arthroplasty and to evaluate its clinical applicability and inter- and intra-observer variation and reliability.

Introduction

The trochlear groove plays a major role in the mechanics and patho-mechanics of the patellofemoral joint. Our primary goal was to compare normal, osteoarthritic and dysplastic PFJs in terms of angles and distances.

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 studied the intra- and interobserver reliability of measurements of the position of the components after total knee replacement (TKR) using a combination of radiographs and axial two-dimensional (2D) and three-dimensional (3D) reconstructed CT images to identify which method is best for this purpose.

A total of 30 knees after primary TKR were assessed by two independent observers (an orthopaedic surgeon and a radiologist) using radiographs and CT scans. Plain radiographs were highly reliable at measuring the tibial slope, but showed wide variability for all other measurements; 2D-CT also showed wide variability. 3D-CT was highly reliable, even when measuring rotation of the femoral components, and significantly better than 2D-CT. Interobserver variability in the measurements on radiographs were good (intraclass correlation coefficient (ICC) 0.65 to 0.82), but rotational measurements on 2D-CT were poor (ICC 0.29). On 3D-CT they were near perfect (ICC 0.89 to 0.99), and significantly more reliable than 2D-CT (p < 0.001).

3D-reconstructed images are sufficiently reliable to enable reporting of the position and orientation of the components. Rotational measurements in particular should be performed on 3D-reconstructed CT images. When faced with a poorly functioning TKR with concerns over component positioning, we recommend 3D-CT as the investigation of choice.

Introduction: Complications following hip resurfacing (HR) occur primarily because of the surgeon’s inability to achieve optimal implant positioning, and the significant learning curve associated with this demanding procedure. Our study sought to look at the impact of navigation technologies on this learning curve.

Materials and Methods: Twenty medical students doing their BSc project took part in the study. Four types of synthetic femurs were used for the study viz., Normal anatomy (11students), Osteoarthritis (5), Coxa Vara and Coxa Valga(2). Each student was allowed to insert the guide wire according to their judgement in the femoral head using 3 systems:

Conventional instrumentation,

This achieved angle was then compared with the angle originally planned for each bone in all three groups using digitizing arm.

Results: The range of error using the conventional method to insert a guide wire was 23deg (range −9 to 14, SD= 6.3), using the CT plan method, it was 22 deg (range −9 to 13, SD=6.6). Using the Navigation method it was 7 deg (range −5 to 2, SD=2.). Students who progressed from conventional through planning to navigation (group 1) were no more accurate than students who went straight to navigation without ever having used conventional instrumentation (group 3). Students produced similar accuracy even in their maiden attempt, on difficult anatomy when provided with navigation technology.

Discussion & Conclusion: This study has shown that motivated and enthusiastic students can achieve an expert level of accuracy very rapidly when provided with the appropriate level of technology. he development of surgeons who are able to deliver excellent outcomes depends more on technology than training.

The rotational alignment of the tibia is an unresolved issue in knee replacement. A poor functional outcome may be due to malrotation of the tibial component. Our aim was to find a reliable method for positioning the tibial component in knee replacement.

CT scans of 19 knees were reconstructed in three dimensions and orientated vertically. An axial plane was identified 20 mm below the tibial spines. The centre of each tibial condyle was calculated from ten points taken round the condylar cortex. The tibial tubercle centre was also generated as the centre of the circle which best fitted eight points on the outside of the tubercle in an axial plane at the level of its most prominent point.

The derived points were identified by three observers with errors of 0.6 mm to 1 mm. The medial and lateral tibial centres were constant features (radius 24 mm (sd 3), and 22 mm (sd 3), respectively). An anatomical axis was created perpendicular to the line joining these two points. The tubercle centre was found to be 20 mm (sd 7) lateral to the centre of the medial tibial condyle. Compared with this axis, an axis perpendicular to the posterior condylar axis was internally rotated by 6° (sd 3). An axis based on the tibial tubercle and the tibial spines was also internally rotated by 5° (sd 10).

Alignment of the knee when based on this anatomical axis was more reliable than either the posterior surfaces or any axis involving the tubercle which was the least reliable landmark in the region.

Introduction: The development of the ilioinguinal approach by the pioneering work of Letournel in 1965 has transformed the treatment of acetabular fractures. To date, this approach has been well established and few modifications have been described of the original approach. However, this approach is difficult, takes long time for exposure and closure of abdominal layers. The aim of this article is to report a modification of the approach which the authors have found particularly useful.

Material and Method: Cadaveric dissection showed that it was easier to detach the inguinal ligament from the anterior superior iliac spine and reflect the anterior abdominal wall as one layer, than by the classical approach through layers of the anterior abdominal wall. Closure was also simpler, in the cadaver, with the entire anterior abdominal wall reattaching satisfactorily by a single transosseous suture. The rest of the approach, including division of iliopectineal fascia and developing the three windows remains the same as in the original approach.

Results: To date, three acetabular fractures have been reduced and fixed using this modification. Besides substantially speeding up the exposure and closure, this approach allows superior distal visualization of the anterior column and wall, and the impression of rather less bleeding. No complications developed with the three cases treated through this modified approach, and specifically, there have been no hernias, nor has the lateral femoral cutaneous nerve of the thigh been damaged.

Discussion: This small study demonstrates a modification to a classic approach that seems to be both safe and fast We hope that further experience will also show reduction in problems associated with wound healing. Further work in progress may also show that femoral venous flow is less impeded by this approach as retraction is not against the unyielding inguinal ligament.

Various frames of reference are routinely used for hip and knee arthroplasty. We hypothesised that the linea aspera is a constant anatomical feature which can be used as a frame of reference.

Twenty cadaveric femora were CT scanned with high resolution 1mm slices. Robin 3D software was used to manipulate the CT data. Three points were identified on the posterior aspect of the lesser trochanter, medial and lateral femoral condyles to position the femora in similar positions based on the posterior femoral plane (PFP). Centres of the femoral head and neck were derived by surface markers placed on the head and around the neck respectively. Joining the 2 centres gave head neck axis (HNA). The most prominent point on the linea aspera was identified at a level midway along the length of the femur. At that level the centre of the canal was derived by placing surface markers. Joining the most prominent point on the linea aspera to the centre of the canal identified our plane, linea aspera – centre plane (LCP). Angle measurements were made between PFP to HNA, PFP to LCP and LCP to HNA.

PFP to HNA is the traditional method for measuring anteversion angle which in our series had a mean of 13°, SD of 5 (range 5–24). PFP to LCP gave very similar results with mean 101°, SD 6 (range 92–112). However it was noted that there is weak correlation between PFP to HNA angle and PFP to LCP angle for each femur. LCP to HNA measurements were more variable with mean 89°, SD 8 (range 76–108).

From these data we conclude that the proximal half of the femur has more variable torsion compared to the distal half. This study shows that the linea aspera should not be used as a frame of reference for hip nor knee arthroplasties. However, further studies are needed to evaluate the linea aspera in-vivo where it is expected to be more prominent and easier to identify.

The use of intramedullary column screws in the treatment of acetabular fractures is becoming more widely utilized. The development of percutaneous methods to insert these screws under image intensifier guidance is one of the main reasons for their increased use. Few groups are navigating insertion of these screws. The available screws are cannulated 6.5–8 mm screws. Most surgeons prefer using 3.2 mm guide wires to reduce deflection. With a shank diameter of 4.5 mm, 3.2 mm cannulation significantly weakens the screws. We postulated that both columns, specially the posterior column can accommodate larger screw diameters which will increase the stability of fixation allowing earlier full weight bearing. The currently used screws were designed for fixation of femoral neck fractures. As percutaneous fixation of acetabular fractures is a growing area of interest, this warrants designing suitable screws with larger diameters.

Eight CT scans of the adult pelvis –performed for non fracture related indications-, were studied (7 females, 1 male). We found that the anatomical cross-section of the columns is irregular but approximately triangular. The method we used to determine the largest diameter of a screw to fit each column was fitting cylinders in the columns. Robin’s 3D software was used to segment acetabula and convert the CT data into polygon mesh (stereolithography STL format) bone surfaces at an appropriate Hounsfield value. The resulting STL files were imported in Robin’s Cloud software, where polygon mesh cylinders of 10 mm diameter were fitted in each column. These cylinders were then manipulated to achieve best fit and their diameters were gradually increased to the biggest diameter which still fitted in the column.

The mean diameters of the fitted cylinders were 10.8 mm (range: 10–13mm) and 15.2 mm (range 14–16.5mm) for the anterior and posterior columns respectively.

To our knowledge, this is the first investigation to study the cross sectional dimensions of the anterior and posterior columns of the acetabulum. Our small sample shows that both columns can safely accommodate larger screws than those currently used. We plan to investigate this further using cadavers.

Various frames of reference are routinely used for hip and knee arthroplasty. We hypothesised that the linea aspera is a constant anatomical feature which can be used as a frame of reference.

Twenty cadaveric femora were CT scanned with high resolution 1mm slices. Robin 3D software was used to manipulate the CT data. Three points were identified on the posterior aspect of the lesser trochanter, medial and lateral femoral condyles to position the femora in similar positions based on the posterior femoral plane (PFP). Centres of the femoral head and neck were derived by surface markers placed on the head and around the neck respectively. Joining the 2 centres gave head neck axis (HNA). The most prominent point on the linea aspera was identified at a level midway along the length of the femur. At that level the centre of the canal was derived by placing surface markers. Joining the most prominent point on the linea aspera to the centre of the canal identified our plane, linea aspera – centre plane (LCP). Angle measurements were made between PFP to HNA, PFP to LCP and LCP to HNA.

PFP to HNA is the traditional method for measuring anteversion angle which in our series had a mean of 13°, SD of 5 (range 5–24). PFP to LCP gave very similar results with mean 101°, SD 6 (range 92–112). However it was noted that there is weak correlation between PFP to HNA angle and PFP to LCP angle for each femur. LCP to HNA measurements were more variable with mean 89°, SD 8 (range 76–108).

From these data we conclude that the proximal half of the femur has more variable torsion compared to the distal half. This study shows that the linea aspera should not be used as a frame of reference for hip nor knee arthroplasties. However, further studies are needed to evaluate the linea aspera in-vivo where it is expected to be more prominent and easier to identify.

Surgeons need to be able to measure angles and distances in three dimensions in the planning and assessment of knee replacement. Computed tomography (CT) offers the accuracy needed but involves greater radiation exposure to patients than traditional long-leg standing radiographs, which give very little information outside the plane of the image.

There is considerable variation in CT radiation doses between research centres, scanning protocols and individual scanners, and ethics committees are rightly demanding more consistency in this area.

By refining the CT scanning protocol we have reduced the effective radiation dose received by the patient down to the equivalent of one long-leg standing radiograph. Because of this, it will be more acceptable to obtain the three-dimensional data set produced by CT scanning. Surgeons will be able to document the impact of implant position on outcome with greater precision.

Massive endoprostheses using a cemented intramedullary stem are widely used to allow early resumption of activity after surgery for tumours. The survival of the prosthesis varies with the anatomical site, the type of prosthesis and the mode of fixation. Revision surgery is required in many cases because of aseptic loosening. Insertion of a second cemented endoprosthesis may be difficult because of the poor quality of the remaining bone, and loosening recurs quickly.

We describe a series of 14 patients with triplate fixation in difficult revision or joint-sparing tumour surgery with a minimum follow-up of four years. The triplate design incorporated well within a remodelled cortex to achieve osseomechanical integration with all patients regaining their original level of function within five months.

Our preliminary results suggest that this technique may provide an easy, biomechanically friendly alternative to insertion of a further device with an intramedullary stem, which has a shorter lifespan in revision or joint-sparing tumour surgery. A short segment of bone remaining after resection of a tumour will not accept an intramedullary stem, but may be soundly fixed using this method.

To assess the performance and success of joint sparing limb salvage surgery in high grade malignancy, in terms of function, complications, recurrence and survival, as compared to joint resection.

We report a ten-year experience of twenty patients with high grade malignancies of bone which did not cross the epiphyseal plate. They underwent not only limb salvage surgery but also joint preservation. The aim of this is to preserve function in the joint and to prevent the inevitable wear of prosthetic joints requiring revision surgery. The age range was 4 - 25 years (mean 13. 5). The Diagnoses were 14 Osteosarcomas and 6 Ewings sarcomas. Mean follow up was 49 months. There were 13 femoral & 7 tibial malignancies. 12 underwent complex biological fixation with a combination of reimplanted autoclaved or irradiated bone; vascularised fibular graft; femoral or humeral allograft. In 8 cases custom made hydroxyapatite coated prostheses were used to replace the resected bone. This surgery must clearly be evaluated in the context of recurrence, particularly as this is associated with an increased risk of metastases and death. Analysis of our results to date has not shown a greater rate of complications. We experienced one recurrence, and one death. The custom prostheses group had fewer complications and operations. Functionally these patients report near normal limbs and joints and do not report any limitation of activities.

Joint sparing limb salvage surgery is extremely worthwhile as it produces a significantly better functioning limb and lower morbidity, with less likelihood of revision surgery. We have not found a higher risk of post-operative complications, recurrence or death. Furthermore massive prosthetic replacement is quicker, osseointegrates reliably and is associated with a lower complication and further operation rate.

We report the results of a prospective study of 23 patients in which interstitial laser photocoagulation (ILP) was used to treat an osteoid osteoma. ILP is a technique in which tumour tissue is destroyed by direct heating using low-power laser light energy delivered by thin (400 μm) optical fibres which are introduced percutaneously into the tumour under image guidance.

Pain was evaluated before operation and at the latest follow-up using a visual analogue scale with 0 denoting no pain and 10 the worst pain imaginable. The mean follow-up was for 15 months.

The results showed that the mean pain score decreased from 7.5 before operation to 0.95 at the latest follow-up. Fourteen patients had no pain and eight had minor discomfort, not requiring analgesia. One patient required a second procedure because placement of the fibre had not been accurate enough and one developed recurrent symptoms eight months after treatment. All patients were satisfied with the operation because of the rapid resolution of pain, the minimally invasive nature of the procedure, and the fact that there was no postoperative restriction of activity.