Jon Clarke

A comparison of radiological and computer navigation measurements of lower limb coronal alignment before and after total knee replacement

We compared lower limb coronal alignment measurements obtained pre- and post-operatively with long-leg radiographs and computer navigation in patients undergoing primary total knee replacement (TKR). A series of 185 patients had their pre- and post-implant radiological and computer-navigation system measurements of coronal alignment compared using the Bland-Altman method. The study included 81 men and 104 women with a mean age of 68.5 years (32 to 87) and a mean body mass index of 31.7 kg/m(2) (19 to 49). Pre-implant Bland-Altman limits of agreement were -9.4° to 8.6° with a repeatability coefficient of 9.0°. The Bland-Altman plot showed a tendency for the radiological measurement to indicate a higher level of pre-operative deformity than the corresponding navigation measurement. Post-implant limits of agreement were -5.0° to 5.4° with a repeatability coefficient of 5.2°. The tendency for valgus knees to have greater deformity on the radiograph was still seen, but was weaker for varus knees. The alignment seen or measured intra-operatively during TKR is not necessarily the same as the deformity seen on a standing long-leg radiograph either pre- or post-operatively. Further investigation into the effect of weight-bearing and surgical exposure of the joint on the mechanical femorotibial angle is required to enable the most appropriate intra-operative alignment to be selected.

Using navigation intraoperative measurements narrows range of outcomes in TKA

Computer-assisted technology creates a new approach to total knee arthroplasty (TKA). The primary purpose of this technology is to improve component placement and soft tissue balance. We asked whether the use of navigation techniques would lead to a narrow range of implant alignment in both coronal and sagittal planes and throughout the flexion-extension range. Using a prospective consecutive series of 57 navigated TKAs, we assessed intraoperative knee measurements, including alignment, varus-valgus stress angles in extension, and varus-valgus angles from 0° to 90° of flexion comparing postimplant with preimplant. We found fewer outliers with coronal (100% of TKAs within ±2°) and sagittal (0% of TKAs with fixed flexion greater than 5°) alignment, soft tissue balancing (mean varus and valgus stress angles −3.2° and 2.3°; range, −5° to 5°), and mean femorotibial angle over flexion range 0° (−0.2°; range, −1° to 2°), 30° (−0.2°; range, −5° to 4°), 60° (−0.5°; range, −5° to 7°), and 90° (−0.2°; range, −5° to 10°). This technology allows a narrow range of implant placement and soft tissue management in extension. We anticipate improved ultimate patient outcomes with less tissue disruption.Level of Evidence: Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

A quantitative method of effective soft tissue management for varus knees in total knee replacement surgery using navigational techniques.

Abstract Total knee replacement (TKR) has become the standard procedure in management of degenerative joint disease with its success depending mainly on two factors: three-dimensional alignment and soft-tissue balancing. The aim of this work was to develop and validate an algorithm to indicate appropriate medial soft tissue release during TKR for varus knees using initial kinematics quantified via navigation techniques. Kinematic data were collected intra-operatively for 46 patients with primary end-stage osteoarthritis undergoing TKR surgery using a computer-tomography-free navigation system. All patients had preoperative varus knees and medial release was made using the surgeons experience. Based on these data an algorithm was developed. This algorithm was validated on a further set of 35 patients where it was used to define the medial release based on the kinematic data. The post-operative valgus stress angles for the two groups were compared. These results showed that the algorithm was a suitable tool to indicate the type of medial release required in varus knees based on intra-operatively measured pre-implant valgus stress and extension deficit angles. It reduced the percentage of releases made and the results were more appropriate than the decisions made by an experienced surgeon.

Non-invasive computer-assisted measurement of knee alignment.

The quantification of knee alignment is a routine part of orthopaedic practice and is important for monitoring disease progression, planning interventional strategies, and follow-up of patients. Currently available technologies such as radiographic measurements have a number of drawbacks. The aim of this study was to validate a potentially improved technique for measuring knee alignment under different conditions. An image-free navigation system was adapted for non-invasive use through the development of external infrared tracker mountings. Stability was assessed by comparing the variance (F-test) of repeated mechanical femoro-tibial (MFT) angle measurements for a volunteer and a leg model. MFT angles were then measured supine, standing and with varus-valgus stress in asymptomatic volunteers who each underwent two separate registrations and repeated measurements for each condition. The mean difference and 95% limits of agreement were used to assess intra-registration and inter-registration repeatability. For multiple registrations the range of measurements for the external mountings was 1° larger than for the rigid model with statistically similar variance (p = 0.34). Thirty volunteers were assessed (19 males, 11 females) with a mean age of 41 years (range: 20–65) and a mean BMI of 26 (range: 19–34). For intra-registration repeatability, consecutive coronal alignment readings agreed to almost ±1°, with up to ±0.5° loss of repeatability for coronal alignment measured before and after stress maneuvers, and a ±0.2° loss following stance trials. Sagittal alignment measurements were less repeatable overall by an approximate factor of two. Inter-registration agreement limits for coronal and sagittal supine MFT angles were ±1.6° and ±2.3°, respectively. Varus and valgus stress measurements agreed to within ±1.3° and ±1.1°, respectively. Agreement limits for standing MFT angles were ±2.9° (coronal) and ±5.0° (sagittal), which may have reflected a variation in stance between measurements. The system provided repeatable, real-time measurements of coronal and sagittal knee alignment under a number of dynamic, real-time conditions, offering a potential alternative to radiographs.

Standardising the clinical assessment of coronal knee laxity

Clinical laxity tests are used for assessing knee ligament injuries and for soft tissue balancing in total knee arthroplasty. This study reports the development and validation of a quantitative technique of assessing collateral knee laxity through accurate measurement of potential variables during routine clinical examination. The hypothesis was that standardisation of a clinical stress test would result in a repeatable range of laxity measurements. Non-invasive infrared tracking technology with kinematic registration of joint centres gave real-time measurement of both coronal and sagittal mechanical tibiofemoral alignment. Knee flexion, moment arm and magnitude of the applied force were all measured and standardised. Three clinicians then performed six knee laxity examinations on a single volunteer using a target moment of 18 Nm. Standardised laxity measurements had small standard deviations (within 1.1°) for each clinician and similar mean values between clinicians, with the valgus laxity assessment (mean of 3°) being slightly more consistent than varus (means of 4° or 5°). The manual technique of coronal knee laxity assessment was successfully quantified and standardised, leading to a narrow range of measurements (within the accuracy of the measurement system). Minimising the subjective variables of clinical examination could improve current knowledge of soft tissue knee behaviour.

Measuring the positional accuracy of computer assisted surgical tracking systems

Computer Assisted Orthopaedic Surgery (CAOS) technology is constantly evolving with support from a growing number of clinical trials. In contrast, reports of technical accuracy are scarce, with there being no recognized guidelines for independent measurement of the basic static performance of computer assisted systems. To address this problem, a group of surgeons, academics and manufacturers involved in the field of CAOS collaborated with the American Society for Testing and Materials (ASTM) International and drafted a set of standards for measuring and reporting the technical performance of such systems. The aims of this study were to use these proposed guidelines in assessing the positional accuracy of both a commercially available and a novel tracking system. A standardized measurement object model based on the ASTM guidelines was designed and manufactured to provide an array of points in space. Both the Polaris camera with associated active infrared trackers and a novel system that used a small visible-light camera (MicronTracker) were evaluated by measuring distances and single point repeatability. For single point registration the measurements were obtained both manually and with the pointer rigidly clamped to eliminate human movement artifact. The novel system produced unacceptably large distance errors and was not evaluated beyond this stage. The commercial system was precise and its accuracy was well within the expected range. However, when the pointer was held manually, particularly by a novice user, the results were significantly less precise by a factor of almost ten. The ASTM guidelines offer a simple, standardized method for measuring positional accuracy and could be used to enable independent testing of tracking systems. The novel system demonstrated a high level of inaccuracy that made it inappropriate for clinical testing. The commercially available tracking system performed well within expected limits under optimal conditions, but revealed a surprising loss of accuracy when movement artifacts were introduced. Technical validation of systems may give the user community more confidence in CAOS systems as well as highlighting potential sources of point registration error.

3D bioactive composite scaffolds for bone tissue engineering

Bone is the second most commonly transplanted tissue worldwide, with over four million operations using bone grafts or bone substitute materials annually to treat bone defects. However, significant limitations affect current treatment options and clinical demand for bone grafts continues to rise due to conditions such as trauma, cancer, infection and arthritis. Developing bioactive three-dimensional (3D) scaffolds to support bone regeneration has therefore become a key area of focus within bone tissue engineering (BTE). A variety of materials and manufacturing methods including 3D printing have been used to create novel alternatives to traditional bone grafts. However, individual groups of materials including polymers, ceramics and hydrogels have been unable to fully replicate the properties of bone when used alone. Favourable material properties can be combined and bioactivity improved when groups of materials are used together in composite 3D scaffolds. This review will therefore consider the ideal properties of bioactive composite 3D scaffolds and examine recent use of polymers, hydrogels, metals, ceramics and bio-glasses in BTE. Scaffold fabrication methodology, mechanical performance, biocompatibility, bioactivity, and potential clinical translations will be discussed.

Direct to Consumer Advertising via the Internet, a Study of Hip Resurfacing

Background and Aims With increased use of the internet for health information and direct to consumer advertising from medical companies, there is concern about the quality of information available to patients. The aim of this study was to examine the quality of health information on the internet for hip resurfacing. Methods An assessment tool was designed to measure quality of information. Websites were measured on credibility of source; usability; currentness of the information; content relevance; content accuracy/completeness and disclosure/bias. Each website assessed was given a total score, based on number of scores achieved from the above categories websites were further analysed on author, geographical origin and possession of an independent credibility check. Results There was positive correlation between the overall score for the website and the score of each website in each assessment category. Websites by implant companies, doctors and hospitals scored poorly. Websites with an independent credibility check such as Health on the Net (HoN) scored twice the total scores of websites without. Conclusions Like other internet health websites, the quality of information on hip resurfacing websites is variable. This study highlights methods by which to assess the quality of health information on the internet and advocates that patients should look for a statement of an “independent credibility check” when searching for information on hip resurfacing.

Locked intramedullary nailing of symptomatic metastases in the humerus

The humerus is a common site for skeletal metastases in the adult. Surgical stabilisation of such lesions is often necessary to relieve pain and restore function. These procedures are essentially palliative and should therefore provide effective relief from pain for the remainder of the patients life without the need for further surgical intervention. We report a retrospective analysis of 35 patients (37 nails) with symptomatic metastases in the shaft of the humerus which were treated by locked, antegrade nailing. There were 27 true fractures (73.0%) and ten painful deposits (27.0%). Relief from pain was excellent in four (11.4%), good in 29 (82.9%) and fair in two (5.7%) on discharge. Function was improved in all but one patient. One case of palsy of the radial nerve was noted. The mean postoperative survival was 7.1 months (0.2 to 45.5) which emphasises the poor prognosis in this group of patients. There were no failures of fixation and no case in which further surgery was required. Antegrade intramedullary nailing is an effective means of stabilising the humerus for the palliative treatment of metastases. It relieves pain and restores function to the upper limb with low attendant morbidity.

Correlation of total knee replacement wound dynamic morphology and dressing material properties

This item discusses correlation of total knee replacement wound dynamic morphology and dressing material properties. It is presented in the program and abstracts of the XXI Congress, International Society of Biomechanics.