Knees with isolated lateral compartment osteoarthritis show a substantial variability in functional knee phenotypes with demographic-specific variations: Phenotypic analysis of 305 knees.

BACKGROUND: The primary aim of this study was to assess and describe the phenotypic variation in the coronal plane of knees affected by isolated lateral compartment osteoarthritis (OA). The secondary aim was to investigate the potential gender-specific and age-related differences in functional knee phenotypes among knees with isolated lateral compartment OA. METHODS: A comprehensive classification system was used to categorize 305 knees with isolated lateral compartment OA based on their mechanical hip-knee-ankle angle (HKA), femoral mechanical angle (FMA), and tibial mechanical angle (TMA). The phenotypic variation of functional knee phenotypes was assessed for the entire cohort and stratified by gender and age category. RESULTS: Among knees with isolated lateral compartment OA, a total of 60 distinct functional knee phenotypes were identified, with phenotype VALHKA6°NEUFMA0°VALTMA3° being the most prevalent (10.8 %). Gender-specific differences were evident, with females exhibiting significantly greater valgus alignment in both mean HKA and TMA values compared with males (HKA: -6.4° vs. -5.4°, respectively; P = 0.02 and TMA 94.4° vs. 89.0°, respectively; P = 0.005). Age-related variations included younger patients predominantly displaying femoral deformities, while older patients primarily exhibited isolated tibial- or combined femoral and tibial deformities. CONCLUSIONS: There is a broad variation of functional knee phenotypes among knees affected by isolated lateral compartment OA, with gender-specific and age-related differences. Recognizing this inherent phenotypic diversity during preoperative planning may facilitate the implementation of tailored approaches that account for the unique characteristics and bony deformities of the individual knee.

Higher incidence of patellar incongruence after under correction of pre-arthritic coronal alignment following medial unicompartmental knee arthroplasty.

PURPOSE: This study aimed to compare patellofemoral joint alignment of knees with restored pre-arthritic coronal alignment versus knees with under- or overcorrection from their pre-arthritic coronal alignment following medial unicompartmental knee arthroplasty (UKA) and evaluate the effect of patellofemoral joint alignment on patient-reported outcomes. METHODS: A retrospective analysis of 517 knees following robotic-arm assisted medial UKA was conducted. Postoperative mechanical hip-knee-ankle angle (mHKA) was compared to estimated pre-arthritic coronal alignment, using the arithmetic hip-knee-ankle angle (aHKA). Knees were considered restored to the pre-arthritic coronal alignment if mHKA was within 2.0° of aHKA (Group 1). Non-restored knees were subdivided into > 2.0° over correction (Group 2), or > 2.0° under correction (Group 3) from the pre-arthritic coronal alignment. Patellar congruence and patellar tilt angles were compared between groups. The Kujala score and Knee Injury and Osteoarthritic Outcome Score for Joint Replacement (KOOS, JR) were analyzed by group. Continuous data was compared using analysis of variance or Kruskal-Wallis tests. Chi-squared tests were used to compare discrete variables. Logistic regressions were conducted to estimate the probability of postoperative patellofemoral malalignment. RESULTS: Group 1 included 357 knees (69.1%), Group 2 included 57 knees (11.0%), and Group 3 included 57 knees (11.0%). The prevalence of postoperative abnormal patellar congruence (i.e. ≥ 17°) was higher in Group 3 at 40.4% (p = 0.009), with a higher odds ratio of having an abnormal patellar congruence angle (2.3, p = 0.01) compared to Group 1. The prevalence of postoperative abnormal patellar tilt (i.e. ≥ 14°) was comparable between groups (n.s.). At mean follow up of 4.4 ± 1.6 years, Kujala was worse in Group 3 (76.6 ± 17.4 compared to 84.0 ± 14.9 and 85.0 ± 14.4 in Groups 1 and 2, respectively; p = 0.006). Mean KOOS, JR outcomes were comparable among groups. No significantly inferior Kujala or KOOS, JR outcomes were observed in patients across all groups with abnormal patellar congruence or tilt angles. CONCLUSION: Knees with under correction from their pre-arthritic coronal alignment following medial UKA were associated with a two-fold higher probability of having postoperative patellofemoral incongruence, as well as inferior mid-term Kujala scores compared to knees with restored pre-arthritic coronal alignment and knees with overcorrection from their pre-arthritic coronal alignment. Patellofemoral incongruence alone did not negatively impact functional outcome scores. LEVEL OF EVIDENCE: IV, case series.

Knees with anteromedial osteoarthritis show a substantial phenotypic variation prior and following medial unicompartmental knee arthroplasty.

PURPOSE: The primary aim of this study was to evaluate the phenotypic variation using the Coronal Plane Alignment of the Knee (CPAK) classification among 1000 knees with anteromedial osteoarthritis (OA) both prior to and following medial unicompartmental knee arthroplasty (UKA). The secondary aim of this study was to investigate whether knees maintained their preoperative CPAK phenotype and to evaluate the phenotypic alterations following medial UKA. METHODS: The CPAK classification was used to analyze 1000 knees that underwent medial UKA as treatment for anteromedial OA. Knees were categorized into nine distinct CPAK phenotypes based on their arithmetic hip-knee-ankle angle (aHKA), which estimates the pre-arthritic alignment, and joint line obliquity (JLO), both pre- and postoperatively. Phenotypic variation was analyzed by sex and age, and the phenotypic alterations following medial UKA were evaluated by phenotype. RESULTS: Preoperatively, CPAK phenotype I had the highest prevalence (45.0%). Among males, the preoperative prevalence of CPAK phenotype I was significantly higher compared to females (53.2% vs. 35.0%, respectively; p ≤ .001), whereas females exhibited a significantly higher occurrence of CPAK phenotype V compared to males (9.8% vs. 4.4%, respectively; p ≤ .015). Following medial UKA, CPAK phenotype II had the highest prevalence (53.3%). Overall, 45.1% of knees maintained their preoperative CPAK phenotype following medial UKA, which was most frequently observed among CPAK phenotype II (67.7%) and III (65.8%). CONCLUSION: There is a substantial variation in CPAK phenotypes among knees with anteromedial OA, as well as following treatment with medial UKA. This variability challenges the assumption of uniform characteristics among knees with an identical wear pattern associated with anteromedial OA and emphasizes the complexity and variability of this specific form of OA. LEVEL OF EVIDENCE: III, Retrospective cohort study.

Characterization of opioid consumption and disposal patterns after total knee arthroplasty.

AIMS: The aim of this study was to determine the general postoperative opioid consumption and rate of appropriate disposal of excess opioid prescriptions in patients undergoing primary unilateral total knee arthroplasty (TKA). PATIENTS AND METHODS: In total, 112 patients undergoing surgery with one of eight arthroplasty surgeons at a single specialty hospital were prospectively enrolled. Three patients were excluded for undergoing secondary procedures within six weeks. Daily pain levels and opioid consumption, quantity, and disposal patterns for leftover medications were collected for six weeks following surgery using a text-messaging platform. RESULTS: Overall, 103 of 109 patients (94.5%) completed the daily short message service (SMS) surveys. The mean oral morphine equivalents (OME) consumed during the six weeks post-surgery were 639.6 mg (sd 323.7; 20 to 1616) corresponding to 85.3 tablets of 5 mg oxycodone per patient. A total of 66 patients (64.1%) had stopped taking opioids within six weeks of surgery and had the mean equivalent of 18 oxycodone 5 mg tablets remaining. Only 17 patients (25.7%) appropriately disposed of leftover medications. CONCLUSION: These prospectively collected data provide a benchmark for general opioid consumption after uncomplicated primary unilateral TKA. Many patients are prescribed more opioids than they require, and leftover medication is infrequently disposed of appropriately, which increases the risk for illicit diversion. Cite this article: Bone Joint J 2019;101-B(7 Supple C):98-103.

Cost effectiveness of patellofemoral versus total knee arthroplasty in younger patients.

AIMS: Patellofemoral arthroplasty (PFA) has experienced significant improvements in implant survivorship with second generation designs. This has renewed interest in PFA as an alternative to total knee arthroplasty (TKA) for younger active patients with isolated patellofemoral osteoarthritis (PF OA). We analysed the cost-effectiveness of PFA versus TKA for the management of isolated PF OA in the United States-based population. PATIENTS AND METHODS: We used a Markov transition state model to compare cost-effectiveness between PFA and TKA. Simulated patients were aged 60 (base case) and 50 years. Lifetime costs (2015 United States dollars), quality-adjusted life year (QALY) gains and incremental cost-effectiveness ratio (ICER) were calculated from a healthcare payer perspective. Annual rates of revision were derived from the National Joint Registry for England, Wales, Northern Ireland and the Isle of Man. Deterministic and probabilistic sensitivity analysis was performed for all parameters against a $50 000/QALY willingness to pay. RESULTS: PFA was more expensive ($49 811 versus $46 632) but more effective (14.3 QALYs versus 13.3 QALYs) over a lifetime horizon. The ICER associated with the additional effectiveness of PFA was $3097. The model was mainly sensitive to utility values, with PFA remaining cost-effective when its utility exceeded that of TKA by at least 1.0%. PFA provided incremental benefits at no increased cost when annual rates of revision decreased by 24.5%. CONCLUSIONS: Recent improvements in rates of implant of survival have made PFA an economically beneficial joint-preserving procedure in younger patients, delaying TKA until implant failure or tibiofemoral OA progression. The present study quantified the minimum required marginal benefit for PFA to be cost-effective compared with TKA and identified survivorship targets for PFA to become both less expensive and more effective. These benchmarks might be used to assess clinical outcomes of PFA from an economic standpoint within the United States healthcare system. Cite this article: Bone Joint J 2017;99-B:1028-36.

Why do patellofemoral arthroplasties fail today? A systematic review.

BACKGROUND: Historically poor results of patellofemoral arthroplasty (PFA) were reported in the setting of isolated patellofemoral osteoarthritis (OA). In order to lower PFA failure rates, it is important to identify failure modes using a standardized method. In this systematic review, PFA failure modes were assessed and compared in early vs. late failures and older vs. recent studies. METHODS: Databases of PubMed, Embase and Cochrane and annual registries were searched for studies reporting PFA failures. Failure modes in studies with mean follow-up <5years were classified as early failures while >5years were classified late failures. Cohorts started before 2000 were classified as older studies and started after 2000 as recent studies. RESULTS: Thirty-nine cohort studies (10 level II and 29 level III or IV studies) and three registries were included with overall low quality of studies (GRADE criteria). A total of 938 PFA failures were included and were caused by OA progression (38%), pain (16%), aseptic loosening (14%) and patellar maltracking (10%). Pain was responsible for most early failures (31%), while OA progression was most common in late failures (46%). In older studies, OA progression was more commonly reported as failure mode than in more recent studies (53% vs. 39%, p=0.005). CONCLUSION: This level IV systematic review with low quality of studies identified OA progression and pain as major failure modes. Reviewing these studies, appropriate patient selection could prevent PFA failures in select cases. Future studies assessing the role of PFA in isolated patellofemoral OA are necessary.

Impingement following anterior cruciate ligament reconstruction: comparing the direct versus indirect femoral tunnel position.

PURPOSE: During anterior cruciate ligament (ACL) reconstruction, authors have suggested inserting the femoral tunnel at the biomechanically relevant direct fibres, but this higher position can cause more impingement. Therefore, we aimed to assess ACL graft impingement at the femoral notch for ACL reconstruction at both the direct and indirect tunnel positions. METHODS: A virtual model was created for twelve cadaveric knees with computed tomography scanning in which a virtual graft was placed at direct and indirect tunnel positions of the anteromedial bundle (AM), posterolateral bundle (PL) or centre of the both bundles (C). In these six tunnel positions, the volume (mm3) and mid-point location of impingement (°) were measured at different flexion angles. RESULTS: Generally, more impingement was seen with the indirect position compared with the direct position although this was only significant at 90° of flexion for the AM position (97 ± 28 vs. 76 ± 20 mm3, respectively; p = 0.046). The direct tunnel position impinged higher at the notch, whereas the indirect position impinged more towards the lateral wall, but this was only significant at 90° of flexion for the AM (24 ± 5° vs. 34 ± 4°, respectively; p < 0.001) and C position (34 ± 5° vs. 42 ± 5°, respectively; p = 0.003). CONCLUSION: In this cadaveric study, the direct tunnel position did not cause more impingement than the indirect tunnel position. Based on these results, graft impingement is not a limitation to reconstruct the femoral tunnel at the insertion of the biomechanically more relevant direct fibres.

Survivorship and functional outcomes of patellofemoral arthroplasty: a systematic review.

PURPOSE: Historically poor results of survivorship and functional outcomes of patellofemoral arthroplasty (PFA) have been reported in the setting of isolated patellofemoral osteoarthritis. More recently, however, fairly good results of PFA were reported, but the current status of PFA outcomes is unknown. Therefore, a systematic review was performed to assess overall PFA survivorship and functional outcomes. METHODS: A search was performed using PubMed, Embase and Cochrane systems, and the registries were searched. Twenty-three cohort studies and one registry reported survivorship using Kaplan-Meier curve, while 51 cohort studies reported functional outcomes of PFA. RESULTS: Twelve studies were level II studies, while 45 studies were level III or IV studies. Heterogeneity was mainly seen in type of prosthesis and year the cohort started. Nine hundred revisions in 9619 PFAs were reported yielding 5-, 10-, 15- and 20-year PFA survivorships of 91.7, 83.3, 74.9 and 66.6 %, respectively, and an annual revision rate of 2.18. Functional outcomes were reported in 2587 PFAs with an overall score of 82.2 % of the maximum score. KSS and Knee Function Score were 87.5 and 81.6 %, respectively. CONCLUSION: This systematic review showed that fairly good results of PFA survivorship and functional outcomes were reported at short- and midterm follow-up in the setting of isolated patellofemoral osteoarthritis. Heterogeneity existed mainly in prosthesis design and year the cohort started. CLINICAL RELEVANCE: These results provide a clear overview of the current status of PFA in the setting of isolated patellofemoral osteoarthritis. LEVEL OF EVIDENCE: IV.

Early functional outcome after lateral UKA is sensitive to postoperative lower limb alignment.

PURPOSE: The predictive role of patient-specific characteristics and radiographic parameters on medial unicompartmental knee arthroplasty (UKA) outcomes is well known, but knowledge of these predictors is lacking in lateral UKA. Therefore, purpose of this study was to assess the predictive role of these parameters on short-term functional outcomes of lateral UKA. METHODS: In this retrospective cohort study, Western Ontario and McMaster Universities Arthritis Index scores were collected at 2-year follow-up (median 2.2 years, range 2.0-4.0 years) in 39 patients who underwent lateral UKA. Patient-specific characteristics included age, BMI and gender, while radiographic parameters included osteoarthritis severity of all three compartments and both preoperative and postoperative hip-knee-ankle alignment. RESULTS: BMI, gender, age and preoperative valgus alignment were not correlated with functional outcomes, while postoperative valgus alignment was correlated with functional outcomes (0.561; p = 0.001). Postoperative valgus of 3°-7° was correlated with better outcomes than more neutral (-2° to 3° valgus) alignment (96.7 vs. 85.6; p = 0.011). Postoperative alignment was a predictor when corrected for patient-specific characteristics (regression coefficient 4.1; p < 0.001) and radiological parameters (regression coefficient 3.8; p = 0.002). CONCLUSIONS: Postoperative valgus alignment of 3°-7° was correlated with the best short-term functional outcomes in lateral UKA surgery, while patient-specific parameters and preoperative alignment were not correlated with functional outcomes. Based on these findings, a surgeon should aim for valgus alignment of 3°-7° when performing lateral UKA surgery for optimal functional outcomes. LEVEL OF EVIDENCE: Prognostic study, Level II.

Patients with isolated lateral osteoarthritis: Unicompartmental or total knee arthroplasty?

BACKGROUND: Lateral unicompartmental knee arthroplasty (UKA) and total knee arthroplasty (TKA) are both reliable treatment options for patients with isolated lateral osteoarthritis (OA). However, studies comparing both procedures are scarce. Aims of this study were to (I) compare short-term functional outcomes following lateral UKA and TKA and (II) assess the role of patient characteristics on outcomes as measured by the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). METHODS: In this retrospective cohort study, 82 patients (48 undergoing lateral UKA and 34 undergoing TKA) were identified that presented with lateral OA and completed the WOMAC. Independent t-tests were used to compare outcomes following lateral UKA and TKA. RESULTS: Mean follow-up was 2.8 years (range: 2.0 - 5.0 years). Preoperatively, no differences between lateral UKA and TKA were seen (50.1±13.5 and 53.3±17.1, respectively, p=0.551). Postoperatively, lateral UKA patients reported better overall outcomes than TKA (90.5±11.7 vs. 81.8±17.9, p=0.017). Subgroup analysis showed better outcomes following lateral UKA than TKA in patients younger than 75 years (92.1±9.9 vs. 81.3±19.6, p=0.014) and in females (91.6±9.9 vs. 81.0±18.2, p=0.014). CONCLUSION: These findings indicate that lateral UKA has superior short-term functional outcomes compared to TKA in patients with isolated lateral OA. Better outcomes were especially seen in younger patients and females. These findings may help orthopedic surgeons choose treatment for patients presenting with lateral OA and optimize treatment for individual patients.

Systematic review of medial versus lateral survivorship in unicompartmental knee arthroplasty.

BACKGROUND: Unicompartmental knee arthroplasty (UKA) has gained popularity in patients with isolated unicompartmental osteoarthritis. To our knowledge no systematic review has assessed and compared survivorship of medial and lateral UKA. We performed a systematic review assessing medial and lateral UKA survivorship and comparing survivorship in cohort studies and registry-based studies. METHODS: A search was performed using PubMed, Embase and Cochrane systems. Ninety-six eligible studies reported survivorship, of which fifty-eight reported medial and sixteen reported lateral UKA survivorship. Nineteen cohort studies and seven registry-based studies reported combined medial and lateral survivorship. RESULTS: The five-year, ten-year and fifteen-year medial UKA survivorship was 93.9%, 91.7% and 88.9%, respectively. Lateral UKA survivorship was 93.2%, 91.4% and 89.4% at five-year, ten-year and fifteen-year, respectively. No statistical difference between both compartments was found. At twenty years and twenty-five years survivorship of medial UKA was 84.7% and 80%, respectively, but no studies reported lateral UKA survivorship at these follow-up intervals. Survivorship of cohort studies was not significantly higher compared to registry-based studies at five years (94.3 vs. 91.7, respectively, p=0.133) but was significantly higher at ten years (90.5 vs. 84.1, p=0.015). CONCLUSION: This is the first systematic review that shows no difference in the five-, ten- and fifteen-year survivorship of medial and lateral UKA. We found a lower survivorship in the registry-based studies compared to cohort studies.

Congruence and joint space width alterations of the medial compartment following lateral unicompartmental knee arthroplasty.

Progressive degenerative changes in the medial compartment of the knee following lateral unicompartmental arthroplasty (UKA) remains a leading indication for revision surgery. The purpose of this study is to evaluate changes in the congruence and joint space width (JSW) of the medial compartment following lateral UKA. The congruence of the medial compartment of 53 knees (24 men, 23 women, mean age 13.1 years; sd 62.1) following lateral UKA was evaluated pre-operatively and six weeks post-operatively, and compared with 41 normal knees (26 men, 15 women, mean age 33.7 years; sd 6.4), using an Interactive closest point algorithm which calculated the congruence index (CI) by performing a rigid transformation that best aligns the digitised tibial and femoral surfaces. Inner, middle and outer JSWs were measured by sub-dividing the medial compartment into four quarters on pre- and post-operative, weight bearing tunnel view radiographs. The mean CI of knees following lateral UKA significantly improved from 0.92 (sd 0.06) pre-operatively to 0.96 (sd 0.02) (p < 0.001) six weeks post-operatively. The mean CI of the healthy control group was 0.99 sd 0.01. Post-operatively, the mean inner JSW increased (p = 0.006) and the outer decreased (p = 0.002). The JSW was restored post-operatively as no significant differences were noted in all three locations compared with the control group (inner JSW p = 0.43; middle JSW p = 0.019, outer JSW p = 0.51). Our data suggest that a well conducted lateral UKA may improve the congruence and normalise the JSW of the medial compartment, potentially preventing progression of degenerative change.

What does it take to have a high-grade pivot shift?

UNLABELLED: The pivot shift is the most specific clinical test to assess pathological knee joint rotatory laxity following ACL injury. This article attempts to describe the anatomic structures responsible for creating a high-grade pivot shift and their potential role in customizing ACL reconstruction. A review of the literature demonstrates that disruption of the secondary stabilizers of anterior translation of the lateral compartment including the lateral meniscus, anterolateral capsule, and IT band contributes to a high-grade pivot shift in the ACL-deficient knee. The morphology of the lateral tibial plateau, including increased posteroinferior tibial slope and small size, can also contribute to high-grade pivot shift. Factors that may decrease the grade of the pivot shift include medial compartment injury, MCL injury, patient guarding, and osteoarthritis. In conclusion, a high-grade pivot shift in the ACL-deficient knee is often associated with incompetence of the lateral soft tissue envelope. Rotatory laxity as assessed by the pivot shift may also be falsely underestimated by concomitant injuries. LEVEL OF EVIDENCE: IV.

Clinical feasibility of a magnetic resonance tracking system to guide the position of the scan plane during physiologic joint motion.

PURPOSE: Unrestricted physiologic joint motion results in multidirectional displacement of the anatomic structures. When performing real-time magnetic resonance (MR) imaging of such a joint motion, continuous adjustment of the scan plane position may be required. The purpose of this study was to evaluate the clinical feasibility of a method to guide the scan plane position during dynamic-motion MR imaging of freely moving joints. MATERIALS AND METHODS: The location of a small tracker device (dedicated hardware) placed on the patient's skin overlying a joint was determined by an ultrashort MR sequence and used to automatically adjust the scan plane position prior to each dynamic-motion MR image. Using a vertically open MR unit, this MR tracking system was applied in ten dynamic-motion MR examinations to evaluate flexion/extension manoeuvres in the weight-bearing knee joint, and in ten dynamic-motion MR examinations of the shoulder joint to evaluate manoeuvres such as internal/external rotation of the humerus, stress testing of the glenohumeral joint and abduction/adduction manoeuvres. Average number of manoeuvre repetitions, total number of images and percentage of useful images per manoeuvre were calculated. Imaging time per scan plane for each manoeuvre was recorded. RESULTS: Average repetition of manoeuvres varied between 1.6 and 5.8, with an average number of 7 to 18 images per manoeuvre. Average percentage of useful images varied between 61% and 89%. Total imaging time per scan plane ranged between 1 min 10 s and 4 min 51 s. CONCLUSIONS: The MR tracking system to guide the slice position for each consecutive dynamic-motion MR image of the freely but slowly moving shoulder or knee joint was feasible for clinical use, providing a high percentage of useful images for each manoeuvre within a clinically acceptable time frame.

Surgical navigation in knee ligament reconstruction.

The use of computer navigation in ACL reconstruction was first established in the mid- 1990s. Initial applications of this new technology focused on improving the accuracy and repeatability of tunnel placement. More recent indications focus on intraoperative assessment of knee ligament dynamic laxity measurements. Computer navigation has been used increasingly as a quantitative measurement tool to assess ACL graft obliquity or visualization of the pivot-shift phenomenon. Applications for PCL and MCL reconstruction have not been extensively studied thus far, although specific isometric or laxity measurements could be performed. Future applications include noninvasive registration techniques to use navigation as a combined preoperative, intraoperative and postoperative measurement tool. The purpose of this review is to provide an overview of the current applications and limitations of navigation in knee ligament reconstruction by reviewing the currently available literature.

Open wedge tibial osteotomies influence on axial rotation and tibial slope.

Inaccurate coronal plane and inadvertent sagittal plane realignment is a common problem after high tibial osteotomies (HTO). While the effects of an HTO on the coronal have been studied extensively, the influence on axial rotation has not been described in detail. The current study examines the effect of HTO on tibial rotation in the axial plane as determined by computed tomography. We hypothesized that high tibial osteotomies have an effect on tibial rotation in the axial plane and that depending on the predefined osteosynthetic implant used, a corresponding change in the tibial slope would occur. HTOs with a tapered 12.5 mm Puddu plate were performed on 13 limbs under computer-navigated control. All limbs were CT scanned before and after the HTO. Using specific software, the CT data was converted into 3D computer models and the following parameters compared: (a) varus-valgus leg alignment; (b) tibial axial rotation; (c) tibial slope (including determination of lateral and medial tibial slope, (d) leg length including determination of the tibial length. Results revealed: (a) a varus-valgus alignment increase of 11 +/- 4.7 degrees (P < 0.005); (b) an axial tibial rotation of 2.7 +/- 6.3 degrees (P < 0.075) occurred with external rotation in 10 out of 13 limbs (12 degrees max external; 9.5 degrees max internal); (c) tibial slope revealed differences of 4.2 +/- 5.9 degrees (P < 0.025); (d) the tibial length increased after HTO by 7.1 +/- 3.7 mm (P < 0.005), while there was no significant change in overall leg length. In summary, tibial rotation does occur in high tibial osteotomies with though the degree of external rotation in this study tended not to be statiscally significant. Tapered implants do not guarantee maintenance of a steady tibial slope, while tibial length changes significantly when HTOs are performed. The combined use of CT and 3D software measurement techniques is reproducible and can be used without any further invasive fixation devices.

Percutaneous bone biopsy. A new application for 3D navigation: a pilot study.

Computer Tomography (CT) guided percutaneous bone biopsy has been established as a minimally invasive method for the rapidly obtaining samples from osseous lesions for histological examination. With this method, an overall accuracy of 90% can be obtained without a significant radiation exposure. The aim of this study was to develop a navigated sleeve for the Jamshidi needle in order to perform navigated, percutaneous bone biopsies with the help of Iso-C-3D. Utilizing this navigated biopsy needle, the procedure was analyzed for several parameters including precision, total operating time, and level of radiation exposure. By using the Iso-C-3D navigation the total operating time was 11.7 min (8-14.3) and radiation exposure was 1.6 (0.67-2.12 min). This study demonstrates that navigated percutaneous bone biopsies can be obtained fast and with low radiation exposure. The feasibility of Iso-C-3D navigated bone biopsies is tempered by the requirement a rigidly fixed dynamic reference frame.

Navigation in ACL reconstruction - comparison with conventional measurement tools.

Restoration of rotational and translational stability is a goal of ACL reconstruction. Intraoperative instability measurements of AP translation and rotation are not well established clinically. We compared navigated measurements of tibial AP translation and rotation with mechanical measuring devices: the KT 1000 and a modified goniometer tool. Tests were repeated with intact and dissected ACLs, and measures of translation and rotation statistically compared. There was no significant difference in AP translation between navigation, 3.2 mm (range 1-6 mm) and the KT 1000, 4.8 mm (range, 4-7 mm) in our experimental set up (p>0.05). Tibial rotation revealed no significant difference, 0.12 degrees (range, 0 degrees -1 degrees ) between navigation and goniometer (p>0.05). Total range of rotation was 4.2 degrees (range, 2 degrees -6 degrees ) in intact and 7.05 degrees (range, 4 degrees -9 degrees ) in dissected ACLs (p<0.05). Stability parameters in ACL navigation can be measured precisely under laboratory conditions and results are not significantly different from mechanical testing devices.

Accuracy analysis of Iso-C3D versus fluoroscopy-based navigated retrograde drilling of osteochondral lesions: a pilot study.

The aim of this pilot study was to evaluate the accuracy of two different methods of navigated retrograde drilling of talar lesions. Artificial osteochondral talar lesions were created in 14 cadaver lower limbs. Two methods of navigated drilling were evaluated by one examiner. Navigated Iso-C(3D) was used in seven cadavers and 2D fluoroscopy-based navigation in the remaining seven. Of 14 talar lesions, 12 were successfully targeted by navigated drilling. In both cases of inaccurate targeting the 2D fluoroscopy-based navigation was used, missing lesions by 3 mm and 5 mm, respectively. The mean radiation time was increased using Iso-C(3D) navigation (23 s; 22 to 24) compared with 2D fluoroscopy-based navigation (14 s, 11 to 17).