Arthritic knees, for the purpose of surgical correction during arthroplasty, are generally thought to be either varus knees or valgus knees and soft tissue releases are done in accordance with the same concept. This view is dependent on the clinical deformity in extended knee and the plain AP radiograph of the extended knee. This concept is now challenged by the observations from our study of the arthritic knee kinematics using computer aided navigation when performing total knee replacement arthroplasty. We performed 283 total knee replacements with computer aided navigation. Imageless navigation was used with Stryker and Orthopilot systems. Bone trackers were fixed to the bones and through real time infrared communication the data was collected. The knee kinematics were recorded before and at the end of surgery. This included measurement of biomechanical axis with the knee extended and then gradually flexed. The effect of flexion on the coronal alignment was recorded real time on the computer. The results were then analysed and compared with plain radiographic deformity on long leg films.

Majority of the knees did not behave in a true varus or valgus fashion. We classified the deformity into different groups depending on the behavior of the knee in coronal plane as it moves from extension to flexion. 2 degree was taken as minimum deviation to signify change, as the knee bends from full extension to flexion. The classification system is as follows

Neutral

Deformity - Varus/Valgus to start with in extension

Gp1

Deformity remains the same as the knee flexes

Gp2

Decreasing deformity but does not reach neutral in flexion

Gp3

Decreasing deformity and crosses to opposite (Varus to valgus or valgus to varus) deformity in flexion

Gp4

Deformity first increases and then decreases but does not reach neutral

Traditional releases of medial or lateral structures without realising the true picture of what happens when the knee is flexed, may not be correct. From our study it is clear that not all arthritic varus or valgus knees behave in the same way. Some of the releases we perform conventionally may not be required or need to be modified depending on the knee kinematics.

The recognition of the correct pattern and severity of deformity in knee osteoarthritis has important implications in its surgical management. Our unit routinely uses standing long leg films and computer navigation. However, these modalities are not widely available and most surgeons rely on clinical assessment and short films. Our experience is that clinical assessment can give the opposite impression of the true deformity pattern particularly among obese patients and there is evidence that short knee films are not reliable. Our study aims to compare clinical, radiographic and computer measurements of knee deformity, assess the influence of Body Mass Index and asses the relationship between coronal and flexion deformity.

We measured 52 consecutive knees prior to arthroplasty using clinical, long leg radiographs and computer navigation methods. Systematic clinical measurement was done with patient standing. Standing radiographs stored in a Picture Archiving System were measured by two independent observers. The senior surgeon performed computer measurement while applying axial load to the foot to simulate weight bearing.

Using long leg films as baseline, clinical and X-ray measurement had a mean error of 0.8° (−12 to +12). Seven clinically valgus knees turned out varus on X-ray. Mean BMI for this group was the same as the rest. Using navigation as baseline, clinical and navigation coronal measurements had a mean error of 0.3° (+9 to −10.5). Four clinically valgus knees turned out varus with navigation. Mean BMI for this group was the same as the rest. Flexion deformity was similar between clinical and computer measurement. Three clinically normal knees showed significant varus in both X-ray and navigation. Compared directly, radiographic and navigation coronal deformity showed significant difference in the degree of deformity but not in the pattern of deformity. There was no correlation between BMI and both the error in clinical assessment of coronal deformity and navigation coronal alignment. If flexion deformity was > 5°, higher BMI indicates higher flexion deformity. There was a weak correlation between navigation coronal and flexion deformity.

Although error in clinical measurement did not reach statistical significance, based on our result, clinical assessment can give an incorrect pattern of deformity in up to 13% and hence should not be the sole basis of assessing deformity. Contrary to expectation, BMI did not influence error of clinical assessment or severity of coronal deformity. It however appeared to influence larger flexion deformities. The discrepancy between radiographic and navigation measurements reflects the absence of true weight bearing with navigation even though we tried to simulate this by applying axial load to the foot.

It is generally accepted that Hip-Knee-Ankle (long-leg) radiographs are a good measurement tool for biomechanical axis of the knee and they have been used as the outcome measure for many studies. Most of the surgeons recommend having pre operative and post operative long leg radiographs for total knee replacement surgery, although practice is not as common. We studied the biomechanical axis on long-leg films and compared it with computer navigation.

The objectives were to find out repeatability of measurements of biomechanical axis with inter observer readings on long leg radiographs and to compare biomechanical axis measurements with Navigation values obtained during total knee replacement surgery.

Our institution routinely uses long-leg radiographs for total knee replacement (TKR) surgery both pre- and post-operatively. A series of 209 patients who had navigated TKR between Jan 2007 and 2008 were selected. Stryker and Orthopilot systems for navigation were used. The intra-operative biomechanical axis measurements from the computer navigation files both pre-and post- implant were recorded. The long leg films were measured with a defined protocol from the digital images on PACS system. Centre of the head of femur was taken as the upper point. For the knee centre the midpoint of a line joining the distal femoral notch centre and upper tibia was used. For the ankle centre midpoint of the upper talar margin was used. An angle between the three points represented the radiological biomechanical axis. To investigate inter-observer error, two observers measured the pre- and post-operative biomechanical axis on long leg radiographs independently on 57 patients.

For the inter-observer measurements on 57 patients, the intraclass correlation coefficient was 0.99 for pre-operative radiographs and 0.98 for post-operative radiographs. Maximum difference between the two observers was 2° in four cases. All other cases showed the same readings or 1° difference.

There was a strong correlation, which was statistically significant, between the pre-operative radiographic and navigated measurements with Pearson correlation coefficient of 0.810 (p< 0.001). The maximum difference between the radiographic and navigated measurement was 24 degrees. The relationship between the postoperative measurements was weaker but statistically significant with Pearson correlation coefficient of 0.323 (p< 0.001). The maximum difference between the two methods of measurement was larger 15.5.

It can be concluded from this study that biomechanical axis on a long leg radiograph is a repeatable measure with good inter-observer correlation.

Although it is statistically significantly correlated with navigated readings, the absolute values may be different with both the methods. This raises the question on the reliability of long leg radiographs for the prediction of true biomechanical axis. Most of the larger value differences had a fixed flexion deformities (9 – 45 degrees). This can affect the readings on the long leg radiographs and make the deformity look either smaller or bigger. Also as our knee kinematic study has proven that the deformity does not remain the same in flexion as it was in extended knee that could also account for the difference in the readings. Other reasons for difference in the pre operative readings could be weight bearing status and surgical opening of the joint before taking the pre operative biomechanical axis measurements. Difference in the post operative readings could be attributed to weight bearing status, time length between navigation and radiographic measurements (6–12 wks), scarring of the soft tissues in the time and flexed posture of knee in the early post operative period.

Total knee arthroplasty (TKA) is one of the commonest orthopaedic procedures. Traditionally the surgeon, based on experience, releases the medial structures in knees with varus deformity and lateral structures in knees with valgus deformity until subjectively they feel that they have achieved the intended alignment. The aim of this prospective study was to record the frequency of medial and lateral releases for computer navigated TKAs.

Seven four consecutive patients operated on by a single surgeon were included in this study. All patients had TKA using either Stryker or Orthopilot computer navigation systems. The implants used were Scorpio NRG or Columbus. The biomechanical axis was taken as the reference for distal femoral and proximal tibial cut. The trans-epicondylar axis was taken as the reference for frontal femoral and posterior condylar cuts. A soft tissue release was undertaken after the bony cuts had been made if the biomechanical axis did not come to within 2° of neutral as shown by computer readings in extension. The post-operative alignment was recorded on the navigation system and also analysed with long leg hip knee ankle radiographs.

There were 43 female and 31 males in the study, 34 left and 40 right knees with an age range of 43 to 87 years. The range of pre-operative deformities on long leg radiographs was 15° varus to 27° valgus with a mean of −5.0° and SD 7.4°. Only two patients needed a medial release. None of the patients needed a lateral release. The fixed flexion deformities needed posterior release. None of the patients needed lateral release for patellar tracking. Post-operative alignment was available for 71 patients. The post implant navigation value was within 2° of neutral in all cases. The mean biomechanical axis on radiographs was 0.1° valgus with a SD 2.1° and range from 6° varus to 7° valgus. From the radiographs six patients were outside the ±3° range.

If one sticks to biomechanical axis and transepicondylar axis as the reference for bony cuts, there will be minimal requirement for medial or lateral soft tissue release. According to our results the use of computer navigation gives a low frequency of medial and lateral release in total knee replacement. Other authors have also found that navigation data can help to give a lower rate of soft tissue release, such as Picard et al. who had decreased their soft tissue release to 25%.

It is generally accepted that Hip-Knee-Ankle (long-leg) radiographs are a good measurement tool for biomechanical axis of the knee and they have been used as the outcome measure for many studies. Most of the surgeons recommend having pre operative and post operative long leg radiographs for total knee replacement surgery, although practice is not as common. We studied the biomechanical axis on long-leg films and compared it with computer navigation. The aims were

To find out repeatability of measurements of biomechanical axis with inter observer readings on long leg radiographs

Our institution routinely uses long-leg radiographs for total knee replacement (TKR) surgery both pre- and postoperatively. A series of 209 patients who had navigated TKR between Jan 2007 and 2008 were selected. Stryker and Orthopilot systems for navigation were used. The intra-operative biomechanical axis measurements from the computer navigation files both pre-and post- implant were recorded. The long leg films were measured with a defined protocol from the digital images on PACS system. Centre of the head of femur was taken as the upper point.

For the knee centre the midpoint of a line joining the distal femoral notch centre and upper tibia was used. For the ankle centre midpoint of the upper talar margin was used. An angle between the three points represented the radiological biomechanical axis. To investigate inter-observer error, two observers measured the pre- and postoperative biomechanical axis on long leg radiographs independently on 57 patients. For the inter-observer measurements on 57 patients, the intraclass correlation coefficient was 0.99 for pre-operative radiographs and 0.98 for post-operative radiographs. Maximum difference between the two observers was 2° in four cases. All other cases showed the same readings or 1° difference. There was a strong correlation, which was statistically significant, between the pre-operative radiographic and navigated measurements with Pearson correlation coefficient of 0.810 (p< 0.001). The maximum difference between the radiographic and navigated measurement was 24 degrees. The relationship between the post-operative measurements was weaker but statistically significant with Pearson correlation coefficient of 0.323 (p< 0.001). The maximum difference between the two methods of measurement was larger 15.5.

It can be concluded from this study that biomechanical axis on a long leg radiograph is a repeatable measure with good inter-observer correlation. Although it is statistically significantly correlated with navigated readings, the absolute values may be different with each method. This raises the question of the reliability of long leg radiographs for the prediction of true biomechanical axis. Most of the larger value differences had a fixed flexion deformities (9 – 45 degrees). This can affect the readings on the long leg radiographs and make the deformity look either smaller or bigger. Also, our knee kinematic study has proven that the deformity does not remain the same in flexion and in the extended knee. This could also account for the difference in the readings. Other possible reasons for differences in the pre operative readings: the weight bearing status and the surgical opening of the joint, before taking the pre operative biomechanical axis measurements. Differences in the post operative readings could be attributed to: weight bearing status, time length between navigation and radiographic measurements (6–12 wks), scarring of the soft tissues in the meantime and flexed posture of knee in the early post operative period.

Introduction: The knee joint replacement arthroplasty is a very successful procedure. Traditionally we aim to perform the arthroplasty and recreate the patients’ biomechanical axis and correct the coronal plain alignment deformity. Unfortunately till recently there was no fine way of controlling the exact alignment and depending on surgeon to surgeon, a valgus (to anatomical axis) of 3 to 7 degrees is aimed for using mechanical intra or extramedullary jigs. On proper measurements only 70–80% of knees achieve the aimed result at best as can be seen in the literature. With the advent of computer aided navigation we can now achieve the desired alignment in a much higher percentage of patients.

Material: We performed 1000 total knee arthroplasties at our hospital. Out of these 500 were performed using computer navigation and 500 using conventional mechanical jigs. Pre op and post op long leg alignment films were taken using standardised method. The data was collected using oxford scores and from computer navigation machines and plain radiographic analysis. The observers doing the radiographic analysis were blinded as to whether the patient had procedure done by conventional means or by computer navigation. Sub grouping of the deformities was done depending on the amount of deformity.

Results: 500 patients had the operation done by conventional means and the other 500 with computer navigation guidance. Further subgroups were made depending on the amount of pre-existing radiological deformity 0–5, 6–10, 11–15 and more than 15 degrees of varus or valgus deformity. The effect of gender, bmi, surgeon experience, clinical oxford score outcome was also considered. It was clear that the patients who had more severe deformities and valgus deformities had better post operative alignments after the procedure was performed with computer navigation as compared with the conventional means. There was statistically significant difference observed between the subgroups.

Discussion: Orthopaedic surgery has improved with technical advancements over the number of years. With any new procedure it takes a long time to shed the old beliefs and adapt the new concepts. While we have plenty of evidence in literature and from our study that computer navigation can give better desired alignment after total knee arthroplasty especially with more severe deformities, it still needs to be taken up by majority of orthopaedic surgeons. Ours is the first study to demonstrate the difference in the specific subgroups.

Introduction: Computer aided surgery has been used in orthopaedics for over a decade now. It has mainly found its use in knee and hip arthroplasty. Its use in other areas is still under development. There has been only one published report in literature on its use in patello femoral joint replacement arthroplasty. We did a study to evaluate its use in patello-femoral arthroplasty.

Methods: A retrospective group of patients was selected who had patello-femoral joint arthroplasty under one of the authors with non navigated standard technique. This was compared with another group which was followed prospectively and had it done with minimally invasive technique using computer aided navigation. The main factors compared were blood loss, incision size and hospital stay.

Results: Thirteen patients had patello-femoral arthroplasty. Seven had with aid of computer aided navigation technique. There was a distinct advantage of computer aided surgery in blood loss, hospital stay and size of incision. It had no bearing on the surgical outcome in short term. Long term results are still awaited.

Conclusion: While our study is only short term and does not have many patients, there seems to be a distinct advantage in terms of hospital stay and size of incision.

Computer aided joint replacement surgery is being used increasingly. It is more commonly used at present in the knee replacement surgery as compared to hip replacement arthroplasty. It is still under developmental phase. The published literature shows there is increased accuracy of the component placement of acetabular cup and femoral stem. We describe the technique for the Stryker navigation system as used in total hip arthroplasty.

The technique used by us presently is an active tracker system. This is a both way communication system of infrared waves between the trackers and the sensors. The trackers are fixed to the bones, then the registration of patient specific anatomy is done and hip arthroplasty is performed with aid of the computer navigation.

The computer navigation gives the values of the component orientation in space. It gives the implant position in the pelvis and femur models generated by the computer but fed in and created by the surgeon. It is important that the data fed to the computer in making the model of pelvis and femur is accurate. It is surgeon dependent. At the end of surgery one can also evaluate impingement and range of motion. It also shows the change in offset of the centre of rotation of the hip as well as leg lengthening. While it can aid in the technical performance it is essential that the surgeon does not go blind to his operating environment as the computer navigation is to help the surgeon, not replace.

Computer aided joint replacement surgery is being used increasingly. It has found its most common use in the total knee replacement arthroplasty. Although the literature has proven its accuracy in the alignment of the components, we still await the long term benefits in terms of patient outcome and longevity of the prosthesis.

The parameters of the alignment are created and fed to the computers, although most of these are based on long term wisdom and on the historical observations rather than on hard scientific studies as to the ideal positioning of the implants for each specific individual. It is therefore important that while using the computer guidance we understand what are the technical assumptions and points based on which the computer is guiding us. A presentation of these will be done mainly based on Stryker knee navigation system.

The use of computer aided joint replacement surgery is increasing exponentially. Its use in hip arthroplasty is still under developmental phase. Although the available literature shows there is increased accuracy of the component placement but there can be a number of factors on which it relies.

We have used the Stryker navigation system to aid in total hip arthroplasty for more than four years. It is improving continuously with time. Still there are many factors which are completely surgeon dependent and which can cause lot of variations in the component placement. Most important factors are the registration of patient anatomy and fixity and immobility of the bone trackers during the procedure. A number of other simple things can produce errors. We carried out some studies to see the effect on navigation values which will be presented. While use of computer navigation can aid greatly in achieving the set goals, it is dependent on surgeon thought process and appropriate implementation of the procedure.

Computer aided joint replacement surgery has become very popular during recent years and is being done in increasing numbers all over the world. The accuracy of the system depends to a major extent, on accurate registration and immobility of the tracker attachment devices to the bone. This study was designed to assess the forces needed to displace the tracker attachment devices in the bone simulators.

Bone simulators were used to maintain the uniformity of the bone structure during the study. The fixation devices tested were 3mm diameter self drilling, self tapping threaded pin, 4mm diameter self tapping cortical threaded pin, 5mm diameter self tapping cancellous threaded pin and a triplanar fixation device ‘ortholock’ used with three 3mm pins. All the devices were tested for pull out, translational and rotational forces in unicortical and bicortical fixation modes. Also tested was the normal bang strength and forces generated by leaning on the devices.

The forces required to produce translation increased with the increasing diameter of the pins. These were 105 N, 185 N, and 225 N for the unicortical fixations and 130N, 200N, 225 N for the bicortical fixations for 3mm, 4mm and 5 mm diameter pins respectively. The forces required to pull out the pins were 1475N, 1650N, 2050N for the unicortical, 1020N, 3044N and 3042N for the bicortical fixated 3mm, 4mm and 5mm diameter pins. The ortholock translational and pull out strength was tested to 900N and 920N respectively and still it did not fail. Rotatory forces required to displace the tracker on pins was to the magnitude of 30N before failure. The ortholock device had rotational forces applied up to 135N and still did not fail. The manual leaning forces and the sudden bang forces generated were of the magnitude of 210 N and 150 N respectively.

The strength of the fixation pins increases with increasing diameter from three to five mm for the translational forces. There is no significant difference in pull out forces of four mm and five mm diameter pins though it is more than the three mm diameter pins. This is because of the failure of material at that stage rather than the fixation device. The rotatory forces required to displace the tracker are very small and much less than that can be produced by the accidental leaning or bang produced by the surgeon or assistants in single pins. Although the ortholock device was tested to 135 N in rotation without failing, one has to be very careful not to put any forces during the operation on the tracker devices to ensure the accuracy of the procedure.

Traumatic rotatory atlanto-axial dislocation and subluxations are rare injuries. The diagnosis is often missed or delayed because of subtle clinical signs. Head tilt makes the interpretation of plain radiographs difficult. Delayed diagnosis often results in chronic instability necessitating surgical stabilization. A hitherto undescribed clinical sign was evaluated which should lead to increased awareness and avoid delay in the diagnosis.

Why a new clinical sign?

Easily missed injury

Methods: This study was carried out between 1997 to 2003. The test was applied to 59 patients presenting in Accident and Emergency. All this patients had head tilt even after the application of a hard cervical collar. All the 59 patients had CT scans to confirm or exclude the diagnosis of Rotatory atlanto axial dislocation/subluxation.

Results: The new clinical sign was found to be positive in all the fourteen patients with atlanto- axial rotatory dislocations/subluxations which was confirmed by CT scan. The test was also found to be positive in 5 patients with unilateral facet joint dislocation. The sensivity of the test in our study was 100%. The specificity was 89%, positive predictive value 0.73, negative predictive value 0.9 (90%).

Conclusion: This new clinical sign may help in early recognition of the injury and also act as an effective screen to indicate which patient needs a CT scan to confirm the diagnosis. This can also be applied in places where the CT scan facilities are not readily available especially in the developing nations.

Purpose of the study: To establish the difference between AO plate osteosynthesis and Elastic Stable Intramedullary Nailing and the long-term outcome.

Design: Prospective randomised study.

Material: During 2000 and 2002 prospective randomised study was carried out where children with diaphysial fracture of long bone was either treated with osteosynthesis with AO plate or ESIN. 32 children had AO plate osteosynthesis and 34 children had ESIN procedure.

Methods: In our series of patients managed with ESIN Nailing 24 had forearm fracture 6 had femur fracture 2 had humeral and 2 had tibial fracture. The other group with AO plate osteosynthesis had 25-forearm fracture 1 humeral fracture 4 tibial fractures and 2 femoral fractures.

Results: The group treated with AO plate osteosynthesis 2 had rotational deformity and rest did well. The recovery period after removal of metal work was longer.

The group treated with ESIN procedure 1 patient fell down and bend the C-Nail, which was straightened in situ, and the fracture healed with slight curvature of the femur, which corrected slowly with growth. The forearm fractures did not have any rotational deformity. The recovery period post removal of the ESIN was very short.

Conclusion: We find that ESIN is a superior procedure for diaphysial fractures of long bone in children and AO plating should only be done in cases where ESIN is not possible.

Introduction: Recently there has been a trend for recommending weight bearing 30û ßexion views as the standard view in place of full extension view for the routine radiography of the Knee. It has been shown that this view can pick up more abnormalities and can show a joint space diminution, which cannot be seen on full extension views. It has not been shown by any study that this is not due to the differential thickness of cartilage in different places on femoral condyle thus implying a natural cause rather than pathological process (abnormal wearing of cartilage) of the observed decrease in joint space. So this prospective randomised double blind study was designed. Methods: 22 patients with arthroscopically proven non osteoarthritic knees were included in the study. Knee radiographs were taken in weight bearing full extension and 30û ßexion PA views. The radiographs were randomised and read by a consultant, registrar & senior house ofþcer. Results: Appropriate statistical tests were applied and results analysed. There was up to 2mm difference in the joint space on the two views. Conclusion: The decrease in the joint space if seen on 30û ßexion views as compared to full extension views may be due to the differential thickness of inherent normal cartilage and so is not always due to a pathological process. Based on this a classiþcation was devised to signify the importance of measured differential thickness in the cartilage of femoral condyle.