Abstract. Aim. This study aims to Inter and intra observer reliability compare, use of a standard goniometer (SG) to measure intermetacarpal angle (degrees) vs use of a new technique of using a digital vernier calliper (DVC) (mm) to measure the distance between the first and second metacarpal head. Method. Maximal active abduction and extension of both thumbs was measured in 20 healthy volunteers on two occasions at least one week apart by two assessors. Results. The inter and intra-observer agreement was higher & the variance of the data was lower using the DVC with the new technique than the SG for both thumb abduction and extension. Additionally, the correlation between measurement of extension and abduction was higher using the DVC than the SG. Conclusion. Whilst both tools provide acceptable intra and inter-observer agreement, the new technique using a DVC is consistently better and more reliable than a SG in measuring thumb abduction and extension. The study also supports our hypothesis that the thumb rotates around the second metacarpal head with a consistent radius

INTRODUCTION. In computer-aided total knee arthroplasty (TKA), surgical navigation systems (SNS) allow accurate tibio-femoral joint (TFJ) prosthesis implantation only. Unfortunately, TKA alters also normal patello-femoral joint (PFJ) functioning. Particularly, without patellar resurfacing, PFJ kinematics is influenced by TFJ implantation; with resurfacing, this is further affected by patellar implantation. Patellar resurfacing is performed only by visual inspections and a simple calliper, i.e. without computer assistance. Patellar resurfacing and motion via patient-specific bone morphology had been assessed successfully in-vitro and in-vivo in pilot studies aimed at including these evaluations in traditional navigated TKA. The aim of this study was to report the current experiences in-vivo in two patient cohorts during TKA with patellar resurfacing. MATERIALS AND METHODS. Twenty patients with knee gonarthrosis were divided in two cohorts of ten subjects each and implanted with as many fixed-bearing posterior-stabilised prostheses (NRG® and Triathlon®, Stryker®-Orthopaedics, Mahwah, NJ-USA) with patellar resurfacing. Fifteen patients were implanted; five patients of the Triathlon cohort are awaiting hospital admission. TKAs were performed using two SNS (Stryker®-Leibinger, Freiburg-Germany). In addition to the traditional knee SNS (KSNS), the novel procedure implies the use of the patellar SNS (PSNS) equipped with a specially-designed patellar tracker. Standard navigated procedures for intact TFJ survey were performed using KSNS. These were performed also with PSNS together intact PFJ survey. Standard navigated procedures for TFJ implantation were performed using KSNS. During patellar resurfacing, the patellar cutting jig was fixed at the desired position with a plane probe into the saw-blade slot; PSNS captured tracker data to calculate bone cut level/orientation. After sawing, resection accuracy was assessed using a plane probe. TFJ/PFJ kinematics were captured with all three trial components in place for possible adjustments, and after final component cementing. A calliper and pre/post-TKA X-rays were used to check for patellar thickness/alignment. RESULTS. This protocol was performed successfully in TKAs, resulting in 30 min longer TKA. Final lower limb misalignment was within 0.5°, resurfaced patella was 0.4±1.2 mm thinner than the native, and patellar cut was 0.4°±4.1° laterally tilted. Final PFJ kinematics was taken within the reference normality in both series. PFJ flexion, tilt and medio-lateral shift range were 66.9°±8.5° (minimum÷maximum, 15.6°÷82.5°), 8.0°±3.1° (−5.3°÷2.8°), and 5.3±2.0 mm (−5.5÷0.2 mm), respectively. Significant (p<0.005) correlations were found between the internal/external rotation of the femoral component and PFJ tilt (R. 2. =0.41), and between the mechanical axis on the sagittal plane and PFJ flexion (R. 2. =0.44) and antero-posterior shift (R. 2. =0.45). Patellar implantation parameters were confirmed by X-ray inspections. Discrepancies in thickness up to 5 mm were observed between SNS- and calliper-based measurements. CONCLUSIONS. These results support relevance/efficacy of patellar tracking in in-vivo navigated TKA and may contribute to a more comprehensive assessment of the original whole knee, i.e. including also PFJ. Patellar preparation would be supported for suitable component positioning in case of resurfacing, but, conceptually, also in not-resurfacing if SNS does not reveal PFJ abnormalities., Using this procedure in the future, TFJ/PFJ abnormalities can be corrected intra-operatively by more cautious bone cut preparation and prosthetic positioning on the femur, tibia and patella

During total knee replacement (TKR), surgical navigation systems (SNS) allow accurate prosthesis component implantation by tracking the tibio-femoral joint (TFJ) kinematics in the original articulation at the beginning of the operation, after relevant trial components implantation, and, ultimately, after final component implantation and cementation. It is known that TKR also alters normal patello-femoral joint (PFJ) kinematics resulting frequently in PFJ disorders and TKR failure. More importantly, patellar tracking in case of resurfacing is further affected by patellar bone preparation and relevant component positioning. The traditional technique used to perform patellar resurfacing, even in navigated TKR, is based only on visual inspection of the patellar articular aspect for clamping patellar cutting jig and on a simple calliper to check for patellar thickness before and after bone cut, and, thus, without any computer assistance. Even though the inclusion in in-vivo navigated TKR of a procedure for supporting also patellar resurfacing based on patient-specific bone morphology seems fundamental, this have been completely disregarded till now, whose efficacy being assessed only in-vitro. This procedure has been developed, together with relevant software and surgical instrumentation, as an extension of current SNS, i.e. TKR is navigated, at the same time measuring the effects of every surgical action on PFJ kinematics. The aim of this study was to report on the first in-vivo experiences during TKR with patellar resurfacing. Four patients affected by primary gonarthrosis were implanted with a fixed bearing posterior-stabilised prosthesis (NRG, Stryker®-Orthopaedics, Mahwah, NJ-USA) with patellar resurfacing. All TKR were performed by means of two SNS (Stryker®-Leibinger, Freiburg, Germany) with the standard femoral/tibial trackers, the pointer, and a specially-designed patellar tracker. The novel procedure for patellar tracking was approved by the local ethical committee; the patients gave informed consent prior the surgery. This procedure implies the use of a second system, i.e. the patellar SNS (PSNS), with dedicated software for supporting patellar resurfacing and relative data processing/storing, in addition to the traditional knee SNS (KSNS). TFJ anatomical survey and kinematics data are shared between the two. Before surgery, both systems were initialised and the patellar tracker was assembled with a sterile procedure by shaping a metal grid mounted with three markers to be tracked by PSNS only. The additional patellar-resection-plane and patellar-cut-verification probes were instrumented with a standard tracker and a relevant reference frame was defined on these by digitisation with PSNS. Afterwards, the procedures for standard navigation were performed to calculate preoperative joint deformities and TFJ kinematics. The anatomical survey was performed also with PSNS, with relevant patellar anatomical reference frame definition and PFJ kinematics assessment according to a recent proposal. Standard procedures for femoral and tibial component implantation, and TFJ kinematics assessment were then performed by using relevant trial components. Afterwards, the procedure for patellar resection begun. Once the surgeon had arranged and fixed the patellar cutting jig at the desired position, the patellar-resection-plane probe was inserted into the slot for the saw blade. With this in place, the PSNS captured tracker data to calculate the planned level of patellar bone cut and the patellar cut orientation. Then the cut was executed, and the accuracy of this actual bone cut was assessed by means of the patellar-cut-verification probe. The trial patellar component was positioned, and, with all three trial components in place, TFJ and PFJ kinematics were assessed. Possible adjustments in component positioning could still be performed, until both kinematics were satisfactory. Finally, final components were implanted and cemented, and final TFJ and PFJ kinematics were acquired. A sterile calliper and pre- and post-implantation lower limb X-rays were used to check for the patellar thickness and final lower limb alignment. The novel surgical technique was performed successfully in all four cases without complication, resulting in 30 min longer TKR. The final lower limb alignment was within 0.5°, the resurfaced patella was 0.4±1.3 mm thinner than in the native, the patellar cut was 1.5°±3.0° laterally tilted. PFJ kinematics was taken within the reference normality. The patella implantation parameters were confirmed also by X-ray inspection; discrepancies in thickness up to 5 mm were observed between SNS- and calliper-based measurements. At the present experimental phase, a second separate PSNS was utilised not to affect the standard navigated TKR. The results reported support relevance, feasibility and efficacy of patellar tracking and PFJ kinematics assessment in in-vivo navigated TKR. The encouraging in-vivo results may lay ground for the design of a future clinical patella navigation system the surgeon could use to perform a more comprehensive assessment of the original whole knee anatomy and kinematics, i.e. including also PFJ. Patellar bone preparation would be supported for suitable patellar component positioning in case of resurfacing but, conceptually, also in not resurfacing if patellar anatomy and tracking assessment by SNS reveals no abnormality. After suitable adjustment and further tests, in the future if this procedure will be routinely applied during navigated TKR, abnormalities at both TFJ and PFJ can be corrected intra-operatively by more cautious bone cut preparation on the femur, tibia and also patella, in case of resurfacing, and by correct prosthetic component positioning

Background. Hip fractures affect 1.6 million people globally per annum, associated with significant morbidity and mortality. A large proportion are extracapsular neck of femur fractures, treated with the dynamic hip screw (DHS). Mechanical failure due to cut-out is seen in up to 7% of DHS implants. The most important predictor of cut-out is the tip-apex distance (TAD), a numerical value of the lag screw”s position in the femoral head. This distance is determined by the psychomotor skills of the surgeon guided by fluoroscopic imaging in theatre. With the current state of surgical training, it is harder for junior trainees to gain exposure to these operations, resulting in reduced practice. Additionally, methods of simulation using workshop bones do not utilise the imaging component due to the associated radiation risks. We present a digital fluoroscopy software, FluoroSim, a realistic, affordable, and accessible fluoroscopic simulation tool that can be used with workshop bones to simulate the first step of the DHS procedure. Additionally, we present the first round of accuracy tests with this software. Methods. The software was developed at the Royal National Orthopaedic Hospital, London, England. Two orthogonally placed cameras were used to track two coloured markers attached to a DHS guide-wire. Affine transformation matrices were used in both the anterior-posterior (AP) and cross table lateral (CTL) planes to match three points from the camera image of the workshop bone to three points on a pre-loaded hip radiograph. The two centre points of each marker were identified with image processing algorithms and utilised to digitally produce a line representing the guide-wire on the two radiographs. To test the accuracy of the system, the software generated 3D guide-wire apex distance (GAD) (from the tip of the guide-wire to a marker at the centre of calibration) was compared to the same distance measured with a digital calliper (MGAD). In addition, the same accuracy value was determined in a simulation scenario, from 406 attempts by 67 medical students. Results. The median absolute inaccuracy of FluoroSim with 270 measurements was 3.35mm (IQR = [1.15mm, 6.53mm]). The absolute inaccuracy showed a graded increase the further away the tip of the guide-wire was from the centre of calibration; MGAD ≤10mm, median absolute inaccuracy = 1.53mm; MGAD 10mm<x≤20mm, median absolute inaccuracy = 4.97mm; MGAD >20mm, median absolute inaccuracy = 7.23mm. Comparison between all three groups reached significance (p < 0.001). In a simulation scenario with medical students, FluoroSim had a significantly greater median absolute inaccuracy of 4.79mm compared to the testing scenario (p < 0.001). Conclusion. FluoroSim is a safe and inexpensive digital imaging adjunct to workshop bones simulation. To our knowledge this technology has not been explored in the context of DHS simulation, and has the potential to be extended to other orthopaedic procedures

Aims

Glenoid bone loss is a significant problem in the management of shoulder instability. The threshold at which the bone loss is considered “critical” requiring bony reconstruction has steadily dropped and is now approximately 15%. This necessitates accurate measurement in order that the correct operation is performed. CT scanning is the most commonly used modality and there are a number of techniques described to measure the bone loss however few have been validated. The aim of this study was to assess the accuracy of the most commonly used techniques for measuring glenoid bone loss on CT.

Objective. The relationship between the index (2D) to ring finger (4D) is one of the most commonly studied anthropometric measures, which is believed to offer insight into early growth and the foetal environment. This study aimed to determine the relationship between the 2D:4D ratio and the risk of Perthes' disease in children. Methods. The 2D:4D ratio was measured in 144 cases of Perthes' disease, and 144 controls. Cases and controls were frequency matched for age and sex. Measurements were recorded using a digital venier calliper on the palmar surface of the hand. Logistic regression was undertaken adjusting for age, with stratification for sex. Results. There was a significant negative association between Perthe's disease and digit ration in the right hand in affected females OR −0.78 (95% CI 0.65 – 0.93). There was no such association in males 0.97 (0.90 – 1.05). Conclusions. There is a significant association between degree of ‘masculinisation’ and Perthes' disease. This adds evidence to suggest that a significant aetiological component in disease acts prenatally, and may begin to explain the preponderance of disease amongst males

Aims: The topographical measurement and representation of the ACL insertion on the tibial plateau, based on a greek population sample. Methods: Fourty eight tibial plateaus were explanted during TKA surgery in 33 female and 15 male patients (average age of 71.2 yrs) suffering from osteoarthritis and rheumatoid arthritis. By means of a calliper, measurements were conducted in order to determine the dimensions shown. Data were used for a topographical representation. Conclusions: To the authors’ best knowledge, this is the first such anthropometric study on a greek population and its results provide a confirmation on the relatively wide base of ACL insertion on the tibial plateau. The biomechanical performance of this natural configuration for a full range of motion, is possibly not sufficiently reproduced by conventional ACL reconstruction techniques using just one bundle

Aims: The topographical measurement and representation of the ACL insertion on the tibial plateau, based on a greek population sample. Methods: Fourty eight tibial plateaus were explanted during TKA surgery in 33 female and 15 male patients (average age of 71.2 yrs) suffering from osteoarthritis and rheumatoid arthritis. By means of a calliper, measurements were conducted in order to determine the dimensions shown. Data were used for a topographical representation. Conclusions: To the authors’ best knowledge, this is the first such anthropometric study on a greek population and its results provide a confirmation on the relatively wide base of ACL insertion on the tibial plateau. The biomechanical performance of this natural configuration for a full range of motion, is possibly not sufficiently reproduced by conventional ACL reconstruction techniques using just one bundle

To determine whether measuring pedicle size on CT is accurate and reproducible using the WEBPACS ruler tool. Radiological analysis. A human cadaveric spine along with 5 geometrical shapes were scanned using a multislice spiral CT scanner with 1mm cuts. The objects and the pedicle diameters for lumbar and thoracic vertebrae in the axial plane were measured independently using the WEBPACS ruler tool by 2 observers (to the nearest 0.1mm). The geometrical shapes and pedicle size on the skeleton were then measured using Vernier callipers by an independent third observer. All measurements were repeated a week later. Reproducibility of the measurements was assessed using Bland and Altman plots. Accuracy was assessed using the Vernier calliper measurements as the gold standard and comparing the plots. Perfect reproducibility was achieved when measuring the geometric objects with the Vernier callipers. The error of the measurement associated when measuring the pedicles was 0.5mm. The error of the measurement for the geometric objects for observers 1 and 2 was 0.5 and 0.6mm respectively, and for the pedicles it was 1.0 and 0.6mm respectively. The WEBPACS ruler on a CT scan is accurate to within 0.5-0.6mm of the true size of an object. The error for pedicle measurements is marginally higher (0.6-1.0mm) and this may reflect the fact that they are ill defined geometric shapes. Measuring pedicle size on CT for surgical planning may have implications for small pedicles when sizing them up for a good screw. Ethics approval None Interest Statement None

Leg length discrepancy (LLD) following total hip arthroplasty (THA) is a well-known and documented phenomenon. LLD can pose a substantial problem for both the patient and the surgeon. Patient dissatisfaction with LLD after THA is the most common reason for litigation against orthopaedic surgeons. Failure to restore limb length may lead to an unstable hip, whereas over-lengthening may cause low back pain, sciatic nerve palsy and early mechanical loosening. Several intra operative techniques both invasive and non invasive have been reported in the literature to over-come LLD during THA. The accuracy of all the methods that measure from pins anchored into pelvis to point on the greater trochanter may be affected by the inherent variability of the leg position when measurements are made. Bending or dislodging the pins and using of calliper devices can be cumbersome during the THA surgery and can compromise the measurements. Hence we describe a simple, safe and reliable intra operative technique to overcome LLD by using a stout braided suture material tied to the stout Judd pin used to retract the soft tissues in posterior approach. Utilising the routine incision for the posterior approach to the hip, this technique can be easily carried out in primary THA surgery as compared to other techniques used to avoid LLD, which require further incision, and specialised equipment which are time consuming, cumbersome and may not be very secure. This technique of using a suture mark over the Judd pin is simple, inexpensive and easily adaptable

Aim: To prospectively compare the quantity of bone removed from the acetabulum in hip resurfacing arthroplasty and uncemented total hip replacements. Methods: Sixty four patients were prospectively enrolled in the study. We compared 32 birmingham hip resurfacing acetabular components with 32 trident uncemented acetabular cups. To assess the pre-reaming size of the acetabulum, and to allow comparison between acetabular sizes, the size of the femoral head was assessed to the nearest millimetre intraoperatively with the use of a measuring calliper. The reamings from the acetabulum were collected. This bone was then dehydrated and defatted with five washes of acetone followed by five washes of diethyl ether. The bone was then placed in a furnace at 200 degrees Celsius until a consistent dry weight was achieved. The size of acetabular component used was recorded in all cases. Results: The mean weight of bone removed from the acetubulum of the resurfacing group was 13.79 g. The corresponding mean weight of bone removed from the acetabulum of the total hip replacement group was 11.71g. Using a non-parametric analysis of covariance (ANCOVA) to account for the covariate of acetabular size, regression analysis indicated no evidence of a difference between the mean bone weight removed in the two groups (p-value of 0.57). Conclusions: Close attention to surgical technique in preparing the femoral head during resurfacing will allow the use of an appropriately small femoral component. If performed accurately this will avoid oversizing the acetabular component and removal of excess bone stock

Leg-length inequality is not uncommon following primary total hip arthroplasty and can be distressing to the patient. An excellent clinical result with respect to pain relief, function, component fixation, range of motion and radiographic appearance can be transformed into a surgical failure because of patient dissatisfaction due to leg-length inequality. Postoperative leg-length discrepancy was determined radiographically for 200 patients who had had a primary custom total hip arthroplasty. In all cases the opposite hip was considered to have a normal joint center. The femoral component was designed and manufactured individually for each patient using screened marker x-rays. A graduated calliper was used at the time of surgery to control depth of femoral component insertion. The transverse acetabular ligament was used to control placement of the acetabular component and therefore restore acetabular joint center. Using this method 94% of subjects had a postoperative leg-length discrepancy that was 6mm or less when compared to the normal side (average, +0.38mm). The maximum value measured for leg-length discrepancy was +/−8mm. We describe a simple technique for controlling leg length during primary total hip arthroplasty and propose an alternative radiographic method for measuring leg-length discrepancy

Aims

This study aimed to establish the optimal fixation methods for calcaneal tuberosity avulsion fractures with different fragment thicknesses in a porcine model.

Introduction: Osteoporosis is one of the major diseases worldwide, affecting millions of elderly people, with severe economical and medical consequences. The most commonly used method for the determination of decreased bone quality is the assessment of Bone Mineral Density, measured by dual X-ray absorptiometry (DXA). However DXA is quantitative and not qualitative index of the bone structure. The purpose of this study was to correlate the bone mineral density measured by DXA with the mechanical properties of the femoral neck. Materials and Methods: Bone mineral density of the proximal femur of 30 patients (27 women, 3 men) undergoing total hip displacement was estimated by DXA. The average age of these patients was 63.7 years. Patients with sort femoral neck or previous surgeries in proximal femur were excluded from the study. After hip replacement bone samples (femoral head and neck) were frozen and stored at −60 °C. A plane bone slice with 6mm thickness was sawed of femoral neck using a double cutting saw. The exact specimen dimensions were measured using a sliding calliper with high accuracy. All bone specimens were destructively tested on a material testing machine, in order to determine the material properties (Young’s modulus and yield stress) of the samples. The maximum available compression load was 100 kN with a load rate of 10 kN/min. The operational parameters and experimental data were fully controlled and handled by a graphical software package. Finally all data were evaluated and statistically analyzed. Results: A strong linear correlation of bone mineral density (T-score) with maximum failure load of samples was noted (R2=0.852). No significant differences in Young’s modulus values, was found between bone samples. Conclusions: Bone mineral density measured by DXA, although has limitations, remain a strong predictor of bone strength in the femoral neck region

A significant number of patients return with persistent symptoms following surgical release of the posterior interosseous nerve for radial tunnel syndrome. The aim of this study was to attempt to explain this fact in anatomical terms by defining the anatomy of the posterior interosseous nerve and its branches in relation to the supinator muscle and arcade of Frohse. Using standard dissection tools 20 preserved cadaveric upper limbs were dissected. The radial nerve and all its branches within the radial tunnel were exposed and a digital calliper was used to measure distances. The bifurcation of the radial nerve to posterior interosseous nerve and superficial sensory branch occurred at a median distance of 4.35mm proximal to the elbow joint-line. The bifurcation was proximal to the joint-line in 11 cases, at the level of the joint-line in one case and distal in eight cases. There was a range of 0–5 branches to the supinator originating proximal to the entry point of the posterior interosseous nerve under the arcade of Frohse at a median distance of 10.27mm (medial branches) or 11.11mm (lateral branches) distal to the elbow join-line. These branches either passed under the arcade of Frohse or entered through the proximal edge of the superficial belly of the supinator. In 10 limbs there was a variable number of branches to the supinator originating under its superficial belly and in five limbs multiple perforating posterior interosseous nerve branches within the muscle were identified. This variation in anatomy we believe may explain the persistence of symptoms following surgical release of the posterior interosseous nerve for radial tunnel syndrome and suggests that careful exploration of all the nerve branches during surgical decompression should be routinely performed

Seven children, aged four to nine years, underwent fibular transfer between 1990 and 2002. Five had chronic osteomyelitis and two had septic compound fractures. Bone defects measured 5 cm to 20 cm. Reconstruction was performed in two stages. Debridement, sequestrectomy, and Gentamycin bead insertion were performed first. Two children required skin grafting and one a gastrocnemius flap. Fibular transfer was performed as a second stage at four to six weeks, when infection was cleared. Through an anterolateral approach the fibula was divided proximally below the physis and transferred from the lateral to the anterior compartment deep to the tibialis anterior muscle belly. The fibula was fixed with screws to the lateral tibial metaphysis in two children, and placed into the medullary canal and fixed with wires in four. Distal procedures were performed in five children. Patients were immobilised in a cast for three to six months until bone healing occurred, after which the bone was supported with a calliper. Follow-up ranged from 11 months to 13 years. All transfers united to the proximal tibia by 12 weeks. Fibular hypertrophy occurred in all children. There was shortening of 3 cm to 10 cm. Equinus deformity occurred in two children and varus of the ankle in three. All are ambulant with boots and crutches. Fibular transfer is a useful salvage procedure and an alternative to ablation in severe tibial infections with defects. It has a free blood supply and hypertrophies with weight-bearing

The treatment of large bony defects following osteomyelitis and trauma with skin damage is challenging. This paper reports the results of fibular transplant for tibial defects. Between 1990 and 2000, five children aged four to nine years were treated. Four had pyogenic osteomyelitis and one a compound fracture with bone loss. All had large wounds on the medial aspect of the tibia. Before reconstruction, conservative treatment lasted five to six months. Sequestrectomy and debridement were performed before fibular transfer. At surgery the fibula was divided below the physis and transferred to the remaining tibia, deep to the tibialis anterior muscle belly. In two cases the fibula was fixed to the lateral aspect of the tibia with screws, and in three into the metaphysis with K-wires. Bone graft was packed around the transfer. Immobilised in a cast for four to six months, the leg was later protected with a calliper. Follow-up ranged from 9 months to 10 years. All children are ambulant, four with callipers and one independently. The latter shows evidence of tibialisation of the fibula. Follow-up continues and the remaining four transfers show solid union and signs of fibular hypertrophy. Osteomyelitis remains a crippling condition that results in bone defects. Fibular transfer is a salvage procedure and an alternative to ablation in cases of severe bone loss with infection and scarring. It should be reserved for difficult cases with extensive defects where conventional bone grafting is not possible

Aims

During total knee replacement (TKR), surgeons can choose whether or not to resurface the patella, with advantages and disadvantages of each approach. Recently, the National Institute for Health and Care Excellence (NICE) recommended always resurfacing the patella, rather than never doing so. NICE found insufficient evidence on selective resurfacing (surgeon’s decision based on intraoperative findings and symptoms) to make recommendations. If effective, selective resurfacing could result in optimal individualized patient care. This protocol describes a randomized controlled trial to evaluate the clinical and cost-effectiveness of primary TKR with always patellar resurfacing compared to selective patellar resurfacing.

Implant malposition remains one of the common causes of total knee replacement (TKR) failure and increased wear. Recent advances in computer technology have made available navigation systems for TKR and other orthopaedic procedures. The purpose of our study was:. to develop a method to assess the accuracy of an image-free TKR navigation system;. to assess its accuracy in a leg with normal or near-normal mechanical axis;. to assess its accuracy in a leg with abnormal mechanical axis. The system chosen was an image-free system based on electromagnetic technology, the MedTronic AxiEM TKR navigation system. To facilitate measurements, an artificial leg (phantom) was constructed from machined Plexiglas with simulated hip and knee joints. Additional joints located at the midshaft of the tibia and femur allowed deformation in the flexion/extension (y), varus/valgus (x) and rotational (z) planes. Using a highly accurate digital calliper unit (FaroARM Technologies, USA) to precisely measure co-ordinates with pre-machined points on the phantom, a software program was developed to convert these local co-ordinates into a determination of actual leg alignment. This technique was verified using repeated measurement with variable coordinates, giving accuracy to within 0.05 of a degree. Simulated procedures were then performed with both normal and abnormal leg mechanical axis. At specific points in the procedure, information was compared between the FaroARM digital measurements and the CAS system. Repeated serial measurements were undertaken. In the setting of normal alignment, accuracy to within one degree was demonstrated. In the setting of abnormal x, y and z plane alignment in both femur and tibia, accuracy to within two degrees was demonstrated. Several clinical studies have been performed to assess the precision of computer navigation in TKR. This study was designed to assess the accuracy of a clinically validated navigation system. The study demonstrates the high level of in-vitro accuracy of the MedTronic AxiEM navigation system in both normal and abnormal mechanical leg alignment settings

A lumbar laminectomy is a commonly performed surgical procedure for the decompression of neural structures. The aim of this human cadaveric study is to establish the extent of pars interarticularis remaining at each lumbar level when a laminectomy is performed to the medial edge of the pedicle. Seven human cadavers with intact lumbar spines were obtained for this study. The lumbar spine was dissected from the body and segmental disarticulation of each level was performed. The isolated lumbar levels had laminectomies performed exposing the neural canal. The vertical alignment of the laminectomy was orientated in line with the medial aspect of the ipsilateral pedicle. The remaining lateral pars interarticularis was measured with a calliper. The procedure was performed bilaterally at each isolated lumbar segment. Five males and two female cadavers with an age range of sixty-eight years to ninety-five years at the time of death. Fourteen lumbar segments of each respective level were available for study except at L5, where only twelve was possible due the presence of a transitional vertebra in one of the specimens. Taken to the nearest mms, the average width of the remnant pars interarticularis at the L1 level was 4 mm, range 3–6 mm (SD 0.95); L2 6 mm, range 5–7 mm (SD 0.77); L3 8mm, range 4–9mm (SD 1.34); L4 11mm, range 9–14 mm (SD 1.31) and L5 16mm, range 13–17 mm (SD 1.15). One way analysis of variance for each of the groups were performed to establish that the difference recorded was greater than that expected by chance (p< 0.05). The results predictably established the gradual narrowing of the pars interarticularis as the levels ascend cranially from L5. The medial wall of the pedicle could be used as an indirect means to establish a satisfactory remnant of the pars interarticularis following a laminectomy in the lower lumbar spine, at the levels of L3 to L5. However in the upper two levels direct visualisation of the pars is recommended