The aim of the study was to investigate rotational behaviour of the arthritic knee before (preimplant) and after (postimplant) total knee replacement (TKR) using (image-free navigation system as a measurement tool which recorded the axial plane alignment between femur and tibia, in addition to the coronal and sagittal alignment as the knee is flexed through the range of motion. The data on the rotation of the arthritic knee was collected after the knee exposure and registration of the lower limb (preimplant data). The position of rotation between the femur and tibia was recorded in 30° flexion, 45°, 60°, 90° and maximum degrees of flexion of the knee. The data was divided into subsets of varus and valgus knees and these were analysed pre and postimplant for their rotational position using SPSS for statistics.

The system was used in 117 knees of which 91 had full data set available (43 male 48 female). These included 71 varus knees, 16 valgus knees and 4 neutral knees to start in extension. Preimplant data analysis revealed there is tendency for the arthritic knees to first go in internal rotation in the initial part of flexion to 30 degrees and then the rotation is reversed back. This happens irrespective of the initial starting rotational relationship between femur and tibia in full extension. This happens in both varus as well as valgus arthritic knees. This trend of internal rotation in this initial part of flexion is followed in TKR as well implanted with fixed bearing CR knees irrespective of the preoperative deformity. Also noteworthy was the difference in rotation at 30°, 60° and 90 degrees of flexion between preimplant and postimplant knees (irrespective of varus and valgus groups).

When calculated at different points of flexion, there was statistically significant difference in the change of rotation at each point of flexion except 45 degree of flexion. The pre-operative values of change in rotation (internal being positive) at each step from the extended position being 5.4° (SD 4.5°) at 30 ° flexion, 4.7°(5.2°) at 45°, 3.6°(6.1°) at 60°, 3.5°(7.2°) at 90° and 4.2°(8.3°) at maximum flexion. Corresponding post-operative rotations were 2.2°(4.8°), 4.1°(6.4°), 6.6°(7.3°), 9.9°(8.8°) and 7.7°(8.9°). There was also an increase in the total range of rotation that the knee goes through after it has been implanted with prosthesis although it may not happen in every knee. This is statistically significant (p value <0.001) and seems more so in valgus group. The rotational movements and interrelationship of the femur and tibia is a complex issue, especially in the arthritic knees. Preimplant arthritic knee behaved generally similarly to normal knees according to the literature. Normal gait pattern demonstrates that the tibia moved through a 4° to 8° arc of internal rotation relative to the femur. The overall range (10.2° =/−4.2°) of knee rotation in this study greater than 8° might be explained by preimplant data acquired after the knee was approached and therefore releasing knee soft tissue envelop. This study confirmed that during the first 30° both varus and valgus knees moved internally. In our study there is increased range of total rotation postimplant (14° =/−6.8°) which may be explained by the fact that the anterior cruciate ligament is lost in all the TKRs and the posterior cruciate ligament may be dysfunctional as well. Thus the constraints on the knee rotation are decreased postimplant leading to increased rotation. We found some difference between varus and valgus post implant knees in that internal rotation seen in initial 30 degrees of flexion is much more pronounced in valgus knees as compared to varus knees (p value <0.001). This study confirmed knee internal rotation in initial stages of flexion, preimplant in arthritic knees during a passive knee flexion assessment. Varus and valgus knee seemed to behave similarly. This mimics the normal knee rotation. Postimplant knees in TKR behave differently.

Total knee arthroplasty (TKA) is a common orthopaedic procedure. 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 hypothesis for this study was that deformed knees do not routinely require releases to achieve an aligned lower limb in TKA.

A single surgeon consecutive cohort of 74 patients undergoing computer navigated TKA was examined. The mechanical axes were taken as the references for distal femoral and proximal tibial cuts. 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 mechanical femoro-tibial (MFT) angle in extension did not come to within 2° of neutral as shown by computer readings. The post-operative alignment was recorded on the navigation system and also analysed with hip-knee-ankle (HKA) radiographs.

The range of pre-operative deformities on HKA radiographs was 15° varus to 27° valgus with a mean of 5° varus (SD 7.4°). Only two patients required a medial release. None of the patients required a lateral release. The post implant navigation value was within 2° of neutral in all cases. Post-operative HKA radiographs was available for 71 patients. The mean MFT angle from radiographs was 0.1° valgus (SD 2.1°). The range was from 6° varus to 7° valgus but only six patients (8.5%) were outside the ±3° range. The kinematic analysis also showed it to be within 2 degrees of neutral throughout the flexion making sure it is well balanced in 88% cases.

This series has shown that over 90% of patients had limbs aligned appropriately without the need for routine soft tissue releases. The use of computer assisted bone cuts leads to a low level of collateral release in TKA.

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%.

Low grade central osteosarcoma is a rare intramedullary bone producing tumour. It accounts for only 1–2% of all osteosarcomas. Due to the indolent nature of low grade central osteosarcoma, achieving a correct and prompt diagnosis is the real challenge both from imaging and histology, particularly as it may resemble a benign condition, i.e. Fibrous Dysplasia.

We have reviewed 15 cases of low grade central osteosarcoma with long term follow-up (2 to 22 years) to identify problems in diagnosis and treatment and to assess outcome.

There were 7 females and 8 males with a mean age of 37 yrs (range 11 to 72 years); 13 cases arose in the lower limb (8 femur, 4 tibia, 1 os calcis), 1 in the pelvis and 1 in the upper limb. The average duration of symptoms prior to presentation was over 2yrs. A primary diagnosis of low grade central osteosarcoma was achieved for only 6 cases (4 open and 2 needle biopsies), in the other 9 the primary diagnoses were GCT, cystic lesion or fibrous lesion (both benign and malignant) and all of them had undergone treatment (usually curettage with or without bone grafting for this). Definitive treatment was with surgery attempting to obtain wide margins. Marginal excision was associated with local recurrence in three cases but there were no local recurrences in patients who had a wide excision, even in those with prior treatment. Only one patient has died following the development of multiple metastases after 9 years. The survival rate is 90% at 15 years.

We present this study to show the difficulties in diagnosing this rare type of osteosarcoma and to highlight the importance of wide surgical margins to obtain local control.

Low grade central osteosarcoma is a rare intramedullary bone producing tumour. It accounts for only 1–2% of all osteosarcomas. Due to the indolent nature of low grade central osteosarcoma, achieving a correct and prompt diagnosis is the real challenge both from imaging and histology, particularly as it may resemble a benign condition, i.e. Fibrous Dysplasia.

We have reviewed 15 cases of low grade central osteosarcoma with long term follow-up (2 to 22 years) to identify problems in diagnosis and treatment and to assess outcome.

There were 7 females and 8 males with a mean age of 37 yrs (range 11 to 72 years); 13 cases arose in the lower limb (8 femur, 4 tibia, 1 os calcis), 1 in the pelvis and 1 in the upper limb. The average duration of symptoms prior to presentation was over 2yrs. A primary diagnosis of low grade central osteosarcoma was achieved for only 6 cases (4 open and 2 needle biopsies), in the other 9 the primary diagnoses were GCT, cystic lesion or fibrous lesion (both benign and malignant) and all of them had undergone treatment (usually curettage with or without bone grafting for this). Definitive treatment was with surgery attempting to obtain wide margins. Marginal excision was associated with local recurrence in three cases but there were no local recurrences in patients who had a wide excision, even in those with prior treatment. Only one patient has died following the development of multiple metastases after 9 years. The survival rate is 90% at 15 years.

We present this study to show the difficulties in diagnosing this rare type of osteosarcoma and to highlight the importance of wide surgical margins to obtain local control.