The measurement of patellar height: a review of the methods of imaging

Does patella alta lead to worse clinical outcome in patients who undergo isolated medial patellofemoral ligament reconstruction? A systematic review

INTRODUCTION

The aim of this systematic review is to determine the effect of patella height on clinical outcomes after isolated MPFL reconstruction for patella instability. Our primary hypothesis is that patients with patella alta report similar outcomes after isolated MPFL reconstruction compared to patients with normal patella height.

METHODS

A review of the literature was performed according to the PRISMA guidelines. PubMed, EMBASE, and the Cochrane Library were searched from inception to January 10th 2018. Studies were identified using synonyms for "medial patellofemoral ligament", "reconstruction" and "patella alta".

RESULTS

The search resulted in 467 reports on PubMed, 175 on EMBASE and 3 on the Cochrane Library. We included and analyzed in detail six studies describing outcomes after isolated medial patellofemoral ligament reconstruction with regard to patellar height. We found that both patients with patella alta and normal patella height reported satisfactory outcomes after isolated medial patellofemoral ligament reconstruction. However, because of applied exclusion criteria in the included studies the total number of patients with severe patella alta was small (13/74 patients with patella alta, 18%).

CONCLUSIONS

Based on the current literature we suggest that additional tibial tubercle distalisation is not mandatory in patients with mild patella alta (Caton-Deschamps Index 1.2-1.4). To assess the best indications for different surgical procedures for patients with patella instability future research is needed to develop a clear and uniform definition of relevant patella alta.

LEVEL OF EVIDENCE

III.

The Effect of Concomitant Arthroscopic Lateral Retinacular Release on Postoperative Patellar Position and Orientation in Open Wedge High Tibial Osteotomy

Purpose

The purpose of this study was to evaluate the effect of concomitant arthroscopic lateral release (LR) in open wedge high tibial osteotomy (OWHTO) by comparing the pre- and postoperative radiological parameters of patellar position and orientation.

Materials and Methods

The study was comprised of 19 knees undergoing OWHTO and concomitant LR and 18 knees undergoing OWHTO alone. Radiological parameters for patellar position and orientation included the Caton-Deschamps index (CDI), Blackburne-Peel index (BPI), patellar tilting angle (PTA), patellar lateral shift (PLS), and patellofemoral distance (PFD), which were evaluated in the preoperative period and at one year after surgery.

Results

Patellar height was significantly reduced after surgery as indicated by the decrease in BPI (p=0.03) in the OWHTO/LR group, and decrease in CDI (p=0.03) and BPI (p=0.04) in the OWHTO alone group. PTA and PLS were significantly reduced after the combined OWHTO/LR procedure (p=0.04 and p=0.04, respectively). By contrast, no significant changes were detected when isolated OWHTO was performed.

Conclusions

OWHTO induced a postoperative decrease in patellar height in both groups. Regarding the change in patellofemoral alignment, concomitant LR in OWHTO significantly decreased lateral patellar tilt and shift, while no significant difference in those parameters were noted in the OWHTO alone knees.

The clinical and radiological results of individualized surgical treatment depending on pathologic abnormalities in recurrent patellar dislocation: low recurrence rate, but unintended patella baja

PURPOSE

To evaluate the clinical and radiological outcomes and chondral lesion change using individualized surgery for recurrent patellar dislocation.

METHODS

A total of 31 knees with recurrent patellar dislocation underwent surgery depending on individual pathologic abnormalities. Pathologic abnormalities including medial laxity, lateral tightness, increased tibial tuberosity (TT)-to-trochlear groove distance (>20 mm), and patella alta (Caton-Deschamps ratio >1.2) were evaluated in each patient. The abnormalities were corrected through medial patellofemoral ligament reconstruction, TT distalization, TT anteromedialization, and lateral retinacula release. The mean follow-up period was 33 months.

RESULTS

There was one recurrent case (3.2%), requiring additional surgery. The mean Kujala scores were significantly (P = 0.002) improved from 75.8 (SD 12.4) to 84.6 (SD 13.1). Tegner scores were significantly improved from 3.7 (range 1-9) to 5.4 (range 2-9) (P < 0.001), as were and visual analogue scale pain scores from 4.7 (SD 2.5) to 2.6 (SD 2.2) (P = 0.001). Caton-Deschamps ratio was significantly decreased from 1.1 (SD 0.2) to 0.9 (SD 0.1) (P < 0.001), regardless of TT distalization. Chondral lesions of the patella and trochlear groove were improved or maintained in 57.1 and 71.4% of patients, respectively.

CONCLUSION

Individualized surgery in recurrent patellar dislocation was effective and safe with a low recurrence rate. However, the possibility of unintended patella baja, which might be related to post-operative anterior knee pain, should be considered.

LEVEL OF EVIDENCE

IV.

Patellar position in patients with patellofemoral syndrome as characterized by anatomo-radiographic study

Objectives

To determine the prevalence of high patella in adult patients with knee pain, and to correlate patellar height with symptoms of patellar instability, episode of patellofemoral dislocation and anterior pain in the knee; and also verify the concordance correlation between the Insall-Salvati and Caton-Deschamps indices.

Method

Cross-sectional study analyzing the medical records of patients with knee pain, using lateral view knee radiographs with 30° degrees of flexion and computed tomography. The values of the Insall-Salvati index and the Caton-Deschamps index were used to determine the patellar height.

Results

A total of 756 records were analyzed, resulting in 140 knees studied, 39% men and 61% women. Both indices produced statistically significant associations for the occurrence of high patella and signs of instability and episodes of dislocation, but there was no significant association for anterior knee pain. The Kappa index obtained when analyzing the concordance correlation between the Insall-Salvati index and Caton-Deschamps index points to a regular association between them.

Conclusion

Patients with high patella present a higher prevalence of instability. Having a high patella has no significant relationship with the presence of anterior knee pain. The Insall-Salvati and Caton-Deschamps indices demonstrate a regular agreement on the presentation of patellar heights results.

Surgical Treatment With Closing-Wedge Distal Femoral Osteotomy for Recurrent Patellar Dislocation With Genu Valgum

BACKGROUND

Closing-wedge distal femoral osteotomy (CWDFO)-combined with medial reefing and lateral release, if necessary- has been used to treat recurrent patellar dislocation (RPD) with genu valgum.

PURPOSE

To evaluate the clinical and radiologic outcomes of surgical treatment with CWDFO for treatment of RPD with genu valgum.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

Fourteen consecutive patients (23 knees) with RPD and genu valgum were treated with CWDFO. Patients with a minimum 2-year follow-up period were eligible for this study. Patients with prior failed surgery were also eligible. Radiographic evaluation was performed with mechanical femorotibial and lateral distal femoral angle. The radiographic parameters presenting patellar positions and pathologic abnormalities associated with RPD were evaluated. Chondral lesion changes in second-look arthroscopic examination were examined, and clinical outcomes (eg, occurrence of redislocation, range of motion, and clinical scores) were assessed pre- and postoperatively at a minimum of 2 years.

RESULTS

At a mean follow-up of 30.7 months (range, 25-62 months), the mean mechanical femorotibial and mechanical lateral distal femoral angles changed significantly from valgus 5° (range, 2°-11°) to varus 3° (2°-11°; P < .001) and from 83° (range, 78°-86°) to 89° (84°-92°; P < .001), respectively. The mean patellar congruence angle improved from 40° lateral (range, 20°-53° lateral) to 4° medial (23° medial to 21° lateral; P < .001), as did the lateral patellofemoral angle from 26° (range, 8°-62°) to 9° (0°-15°; P < .001). Computed tomography scans showed that the mean distance of patellar lateral shift decreased from 13.5 mm (range, 4-22 mm) to 2.0 mm (-4 to 5 mm; P < .001). The mean tibial tubercle to trochlear groove distance significantly decreased from 20.4 to 13.5 mm ( P < .001), while the Caton-Deschamps ratio did not change significantly after surgery ( P = .984). Chondral lesions of the patella and trochlear groove significantly improved or were maintained. None of the patients experienced subluxation or redislocation after surgery. Patellar instability symptoms also improved, as validated by radiographic and other clinical outcomes.

CONCLUSION

CWDFO combined with medial reefing and lateral release successfully treated RPD with genu valgum for a minimum follow-up of 2 years, with improved patellar alignment and stability.

Normal values of 3 methods to determine patellar height in children from 6 to 12 years

The aim of the study was to compare three methods for high-score measurement in children, Caton-Deschamps, Blackburne-Peel and Koshino-Sugimoto, to determine the normal value of each method in a group of normal children.

MATERIALS AND METHODS

A cross-sectional study on knee x-rays of normal children. Three orthopaedic surgeons measured the Caton-Deschamps, Blackburne-Peel and Koshino-Sugimoto indices. Concordance was assessed using the intraclass correlation coefficient. For interobserver variability, the measurements of each observer for each index were compared and for intraobserver variability, the coefficient between the 2 measurements was calculated by the same observer at 2 different times.

RESULTS

140 knee X-rays divided into 4 age groups were obtained. For the Blackburne-Peel index, an average median of the 3 observers was obtained of 1.07 and with P5-P95 (0.76-1.60). For the Caton-Deschamps index, an average median of the three observers of 1.22 was obtained and with P5-P95 (0.91-1.70). For the Koshino-Sugimoto index, we obtained an average median of the 3 observers of 1.16 and with P5-P95 (0.99-1.36).

DISCUSSION

This study shows that the Koshino-Sugimoto index had the highest reliability, reproducibility and similarity in the population studied, both intra-observer and inter-observer. The other methods evaluated also had variability indices to be taken into account, but were inferior to the Koshino-Sugimoto index.

The quadriceps active ratio: a dynamic MRI-based assessment of patellar height

INTRODUCTION

Patella alta (PA) is one of the primary correctable risk factors for patellofemoral instability (PFI). Both an accurate diagnosis of PA and a clinically relevant target for correction are necessary for optimal treatment. An ideal test for PA should relate the position of the patella to the femur rather than tibia, should do so with the quadriceps contracted and the patellar tendon under tension and should have good sensitivity and specificity. None of the currently used radiographic tests PA meet these criteria, most of which are based on the position of the patella relative to the tibia with diagnostic cutoffs based on 2 standard deviations from the mean rather than optimal sensitivity and specificity. The authors describe the quadriceps active ratio (Q+R), an MRI-based assessment of PA based on patellofemoral contact under quadriceps activated with a cutoff based on optimal sensitivity a specificity for PFI.

MATERIAL-METHODS

Ninety-four participants investigated for knee pain or instability with a clinically indicated MRI were recruited. Routine MRI sequences were obtained, with the addition of a quadriceps contracted sagittal T1-weighted sequence. Participants presenting with PFI were identified. Those with trochlear dysplasia were identified and excluded from analysis so that patellar height could be assessed against PFI without being confounded by trochlear dysplasia. Q+R and patellotrochlear index (PTI) were calculated from the remaining 78 scans by 3 consultant orthopaedic surgeons at three time points. In 54 of these cases, a lateral radiograph was available from which the Insall-Salvati, modified Insall-Salvati, Caton-Deschamps and Blackburn-Peel ratios were also calculated. Intra- and inter-observer reliability was assessed for the Q+R. A cutoff value for the Q+R based on optimal sensitivity and specificity for the diagnosis of PFI was calculated from receiver-operator characteristic (ROC) curves and compared to the PTI. The cutoff for the Q+R was compared for sensitivity and specificity for the diagnosis of PFI against the radiographic ratios.

RESULTS

The Q+R had satisfactory or better ICC values across time points and surgeons. The Q+R was superior to the PTI on area under curve ROC analysis (0.76 vs 0.74). A cutoff value of 0.12 for the Q+R gave sensitivity of 79% and specificity of 55% for the diagnosis of PFI. The radiographic indices were generally insensitive for this diagnosis of PFI with sensitivities ranging from 0-66%.

CONCLUSION

The Q+R is a reliable diagnostic test for patellar height assessment, showing good intra- and inter-rater consistency, and greater diagnostic accuracy than the PTI. A Q+R value of 0.12 is a good test for clinically significant PA. Of the radiographic indices, the Insall-Salvati ratio had the best diagnostic accuracy.

Dynamic tracking influenced by anatomy following medial patellofemoral ligament reconstruction: Computational simulation

BACKGROUND

Continued patellar instability can occur following medial patellofemoral ligament (MPFL) reconstruction. Computational simulation of function was used to investigate the influence of the lateral position of the tibial tuberosity, trochlear dysplasia and patella alta on lateral patellar tracking following MPFL reconstruction.

METHODS

Multibody dynamic simulation models were developed to represent nine knees being treated for recurrent patellar instability. Knee extension against gravity and dual limb squatting were simulated with and without simulated MPFL reconstruction. Graft resting lengths were set to allow 10mm and five millimeters of patellar lateral translation at 30° of knee flexion. The bisect offset index, lateral tibial tuberosity to posterior cruciate ligament tibial attachment (TT-PCL) distance, lateral trochlear inclination, and Caton-Deschamps index were quantified at every five degrees of knee flexion to characterize lateral tracking, lateral position of the tibial tuberosity, trochlear dysplasia, and patella alta, respectively. For the pre-operative and post-operative conditions and each type of motion, bisect offset index was correlated with the anatomical parameters using stepwise multivariate linear regression.

RESULTS

For both motions, the pre-operative and post-operative bisect offset indices were significantly correlated with lateral trochlear inclination and lateral TT-PCL distance. For both motions, the adjusted r² decreased with MPFL reconstruction, but was still approximately 0.5 for MPFL reconstruction allowing five millimeters of lateral translation.

CONCLUSION

MPFL reconstruction decreases but does not eliminate lateral maltracking related to trochlear dysplasia and a lateralized tibial tuberosity. Patients with these pathologies are likely at the highest risk for instability related to maltracking following MPFL reconstruction.

Relationship between radiographic patella-alta pathology and walking dysfunction in children with bilateral spastic Cerebral Palsy

BACKGROUND

Patella-alta is very common in patients with Cerebral Palsy (CP). While several diagnostic x-ray indices have been developed for patella-alta in general, the specific relationship with walking dysfunction in CP is only partly understood.

METHODS

33 participants with bilateral spastic CP between 4 and 20 years (GMFCS I-II without previous surgery) that underwent 3D gait analysis as well as a radiographic exam within 0.8 (SD 1.2) months were retrospectively included. The Caton-Deschamps, the Insall-Salvati and the Koshino-Index, as well as the moment-arms of the quadriceps, the pattelar-tendon length and patellar tilt angle were analyzed from x-rays. During gait, tempo-spatial parameters, the knee flexion kinematics, the knee moments and the moment impulse were calculated and correlated to x-ray parameters.

RESULTS

Smaller quadriceps moment-arms were related to slower walking speed (r=0.48, P=0.005) and less knee extension during stance (r=0.68 P<0.001). Smaller quadriceps moment arms and longer patellar-tendons were also significantly related to a larger knee flexion moment impulse in the second half of the stance phase (r=-0.36, P=0.045 and r=0.39, P=0.028) and hence to more abnormal knee loads. Yet, none of the traditional indices was related to any parameter of gait.

INTERPRETATION

Traditional radiographic indices for patella-alta possess little to no informative value for walking dysfunction in individuals with CP suspected to have knee pathology. Smaller moment-arms are a key feature of patellofemoral pathology in CP reducing the knee extensor mechanism, an aspect which is not sufficiently picked up by traditional indices.

Coronal femoral TKA position significantly influences in vivo patellar loading in unresurfaced patellae after primary total knee arthroplasty

PURPOSE

As patellar tracking and loading is influenced by tibial tuberosity and trochlear groove (TT-TG) distance, patellar height, thickness and tilt as well as TKA component position, it was our hypothesis that these parameters significantly correlate with patellar BTU intensity and localization in SPECT/CT. The purpose of the study was to investigate whether TKA component position as well as the height, thickness and tilt of the unresurfaced patella influences the intensity and the distribution pattern of BTU in SPECT/CT.

METHODS

A total of 62 consecutive patients who underwent primary TKA without patellar resurfacing were prospectively included. Demographic data such as age, gender, side and type of primary TKA were noted. All patients underwent clinical and radiological examination in a specialized knee clinic, including standardized radiographs (anterior-posterior and lateral weight bearing, patellar skyline view) and Tc-99m-HDP-SPECT/CT before, 12 and 24 months after TKA. SPECT/CT images were analysed on 3D reconstructed images. Rotational, sagittal and coronal position of the tibial and femoral TKA components was assessed using a previously validated analysis software. Measurements of BTU including intensity and anatomical distribution pattern were also performed from 3D data. The patellar height, thickness and tilt were measured, and the distance between TT and TG was measured using axial CT images. Univariate analysis was performed to identify any correlations between BTU and TKA component position and patellar measurements (p < 0.05).

RESULTS

The highest median BTU was measured in the superior posterior parts of the patella. A statistically significant correlation was found between valgus alignment of the femoral TKA and increased BTU at the lateral patellar regions (p < 0.05). External rotation of the tibial TKA correlated with increased BTU at the lateral superior joint adjacent part (p < 0.05). No correlation was found between the tibial TKA position (varus-valgus, anterior and posterior slope), TT-TG distance, patellar height and patellar BTU values.

CONCLUSIONS

A significant correlation of increased patellar BTU was found with femoral valgus TKA alignment. These findings highlight the importance of femoral TKA position in coronal plane with regard to post-operative patellar tracking. Moreover, these facts might explain anterior knee pain in unhappy TKA with femoral valgus alignment.

LEVEL OF EVIDENCE

Diagnostic study, Level II.

No change in patellar height following open wedge high tibial osteotomy using a novel femur-referenced measurement method

BACKGROUND

Open wedge high tibial osteotomy (HTO) can influence the tibial slope and thereby the landmarks of currently used patellar height indices. The purpose of this retrospective study was to compare and validate a new femur-referenced patella height measurement method to currently used patellar height indices in a cohort of HTO patients.

METHODS

Patellar height (Caton-Deschamps, Blackburne-Peel and Insall-Salvati Indices and our newly developed Femoral Patellar Height Index) as well as tibial slope were analysed. Full-weight-bearing long-leg anteroposterior radiographs as well as anteroposterior and lateral radiographs of the knee in 0° of extension were used. Radiographs were performed preoperatively, and at six weeks, three, six, 12 and 18months postoperatively. Measurements were recorded twice by two observers. The second observation was performed after a delay of three months.

RESULTS

A total of 99 patients with a mean age of 46.2±8years were included. A statistically significant pre- to postoperative increase in tibial slope was found in all methods. Patellar height decreased according to Caton-Deschamps and Blackburne-Peel Indices. The Insall-Salvati Index as well as the novel Femoral Patellar Height Index remained unchanged. Intra-rater (interclass correlation coefficient (ICC) 0.914-0.998) and inter-rater (ICC 0.955-0.989) reliability were highest in the new index.

CONCLUSION

Detected changes of patellar height following open wedge HTO depend on the method used. Tibial slope increases following surgery. Our new index with a femoral reference for measuring patellar height was validated and good to excellent intra- and inter-rater reliability were demonstrated. Following HTO, the Femoral Patellar Height Index can be recommended as a standardized method to measure patellar height.

An analysis of knee anatomic imaging factors associated with primary lateral patellar dislocations

PURPOSE

Various knee anatomic imaging factors have been historically associated with lateral patellar dislocation. The characterization of these anatomic factors in a primary lateral patellar dislocation population has not been well described. Our purpose was to characterize the spectrum of anatomic factors from slice imaging measurements specific to a population of primary lateral patellar dislocation. A secondary purpose was to stratify these data by sex/skeletal maturity to better detail potential dimorphic characteristics.

METHODS

Patients with a history of primary lateral patellar dislocation between 2008 and 2012 were prospectively identified. Ten MRI measurements were analysed with results stratified by sex/skeletal maturity. A '4-factor' analysis was performed to detail the number of 'excessive' anatomic factors within a single individual.

RESULTS

This study involved 157 knees (79 M/78 F), and 107 patients were skeletally mature. The measurements demonstrate more anatomic risk factors in this population than historical controls. Patella height and trochlear measurements are the most common 'dysplastic' anatomic factors in this population. There were differences based on sex for some patellar height measurements and for TT-TG; there were no differences based on skeletal maturity.

CONCLUSION

Primary lateral patellar dislocation patients have MRI measurements of knee anatomic factors that are generally more dysplastic than the normal population; however, there is a broad spectrum of anatomic features with no pattern predominating. Characterizing knee anatomic imaging factors in the patient with a primary lateral patellar dislocation is a necessary first step in characterizing the (potential) differences between the primary and recurrent patellar dislocation patient.

LEVEL OF EVIDENCE

IV.

Medial patellofemoral ligament reconstruction: patient selection and perspectives

Patellofemoral instability is a painful and often recurring disorder with many negative long-term consequences. After a period of failed nonoperative management, surgical intervention has been used to reduce the incidence of patellar subluxation and dislocations. Medial patellofemoral ligament (MPFL) reconstruction successfully addresses patellofemoral instability by restoring the deficient primary medial patellar soft tissue restraint. When planning MPFL reconstruction for instability, it is imperative to consider the patient's unique anatomy including the tibial tuberosity-trochlear groove (TT-TG) distance, trochlear dysplasia, and patella alta. Additionally, it is important to individualize surgical treatment in the skeletally immature, hypermobile, and athletic populations.

Comparative Study on Insall-Salvati Index by Radiological and Clinical Methods in a Tertiary Care Centre of North Bengal, India

INTRODUCTION

Patellar height is an important parameter of patellar stability. Its importance is evident from various attempts to measure it, by different scientists from time to time and many indices have been derived among which Insall-Salvati index (IS index) is the most simple, accurate and easy to measure. In this study a new clinical method has been tried to measure patellar height by applying the same principle of IS index.

AIM

To compare clinical method of measurement of IS index with the one derived radiologically and to establish the higher cut off value of the clinical method.

MATERIALS AND METHODS

In the present study 186 knee joints (93 subjects) were subjected to measurement of patellar height by both clinical and radiological methods. The IS index was measured bilaterally from lateral view of X-ray plates and it was measured clinically in every knee joint. Both the values were compared using students t-test and higher cut off values were set for normal knee joint for the clinical method.

RESULTS

Among 93 study participants majority were females (54.83%), age of the patients varied from 10-68 years with mean age of 28 years and Standard deviation (SD) of 16.4. It was found that, there was no statistically significant difference between the mean values obtained by clinical method of measurement, compared to conventional one (IS Index) for both the genders and age groups on both the sides. A cut off value of 0.98 cm by clinical method gives sensitivity of 80% and specificity of 36% with area under the ROC curve 0.596.

CONCLUSION

The subjects with patellar height of less than cut off value by clinical method can avoid radiological investigation as there was no statistically significant difference of IS index between radiological and clinical methods.

Patellar Height After Total Knee Arthroplasty: Comparison of 3 Methods

BACKGROUND

Total knee arthroplasty (TKA) is the gold standard procedure for knee osteoarthritis. However, there have been conflicting reports concerning whether TKA is associated with modifications in patellar height. This controversy might be partially explained by the diversity of methods used to measure patellar height. Therefore, we aimed at assessing the reproducibility of 3 radiological indices commonly used to evaluate patellar height-Insall-Salvati (IS), Blackburne-Peel (BP), and Caton-Deschamps (CD) ratios. Additionally, we aimed at evaluating the short-term differences between preoperative and postoperative patellar heights as measured by those 3 methods.

METHODS

Patellar heights were blindly measured by 2 researchers using IS, BP, and CD ratios in 203 knees. Interobserver agreement was evaluated by determination of intraclass correlation coefficients (ICC) and Bland-Altman plots. Preoperative and postoperative patellar heights were compared with Wilcoxon test. The association between postoperative pain and modifications in patellar height was assessed using Mann-Whitney U test.

RESULTS

High interobserver agreement was found for IS (preoperative and postoperative ICC = 0.93), BP (preoperative ICC = 0.89; postoperative ICC = 0.91), and CD (preoperative ICC = 0.89; postoperative ICC = 0.90) ratios. Preoperative and postoperative patellar heights were not significantly different whatever the method used. Postoperative pain was reported after 23% procedures and was significantly associated with wider patellar height variations as measured by the BP ratio (P = .018).

CONCLUSION

The methods evaluated appear to be reproducible. Although patellar height tended to be lower when measured postoperatively, this difference was not significant for any of the methods studied.

Effect of proximal translation of the osteotomized tibial tuberosity during tibial tuberosity advancement on patellar position and patellar ligament angle

Background

Cranial cruciate ligament insufficiency is a common orthopaedic problem in canine patients. This cadaveric and radiographic study was performed with the aim of determining the effect of proximal translation of the tibial tuberosity during tibial tuberosity advancement (TTA) on patellar position (PP) and patellar ligament angle (PLA).

Results

Disarticulated left hind limb specimens harvested from medium to large breed canine cadavers (n = 6) were used for this study. Limbs were mounted to Plexiglass sheets with the stifle joint fixed in 135° of extension. The quadriceps mechanism was mimicked using an elastic band. Medio-lateral radiographs were obtained pre-osteotomy, after performing TTA without proximal translation of the tibial tuberosity, and after proximal translation of the tibial tuberosity by 3mm and 6mm. Radiographs were blinded to the observer for distance of tibial tuberosity proximalization following radiograph acquisition. Three independent observers recorded PP and PLA (tibial plateau method and common tangent method). Comparisons were made between the stages of proximalization using repeated measures ANOVA. Patellar position was found to be significantly more distal than pre-osteotomy, if the tibial tuberosity was not translated proximally (P = 0.001) and if it was translated proximally by 3mm (P = 0.005). The difference between pre-osteotomy PP and 6mm proximalization was not significant. The PLA was significantly larger if the tibial tuberosity was not translated proximally compared to tibial tuberosity proximalization of 6mm using the tibial plateau and the common tangent methods (P = 0.006 and P = 0.015 respectively).

Conclusions

Proximalizing the tibial tuberosity during TTA helps in maintaining vertical position of the patella in the patellar groove. Proximalization of the tibial tuberosity reduces PLA when compared to TTA without tibial tuberosity proximalization.

Patellar height assessment in total knee arthroplasty: a new method

INTRODUCTION

We described in 1981 a method to evaluate patellar height in normal and symptomatic knees on sagittal X-ray view. This index is a frequently used method, yet it is not suitable after a total knee arthroplasty (TKA).

MATERIAL AND METHOD

The original method measures the distance between the distal margin of the articular surface of the patella (point A) and the anterosuperior angle of the tibial plateau (point T), then the length of the patellar articular surface (AP). The index is AT/AP ratio (normal values range from 0.8 to 1.2). After TKA, the T landmark is no longer available, so we must define a new T' landmark. This point is situated at the intersection between the line perpendicular to the tibial posterior cortex elevated at the tip of the fibular head and the tibial anterior cortex. This remarkable landmark can be identified before and after TKA, with a new relative index AT'/AP ratio. This modified method allows the comparison of patella height before and after TKA.

RESULTS

We have used this modified index with the collaboration of several authors during the testing of different models of TKA, with an accurate reproducibility. Repeatability (usually called intra-observer reliability) was good, with intra-class correlation coefficients (ICCs) between 0.58 and 0.75 among the observers. Reproducibility (usually called inter-observer reliability) was also considered as good, with ICC ranging from 0.64 to 0.72.

DISCUSSION

Patella height measurement has to be assessed with the original method (AT/AP) to detect patella infera that could influence the surgical approach. The correlation between original and modified indexes has to be assessed. The modification of patella height after TKA could be evaluated through the modified index and compared with functional results.

PLATEAU-PATELLA ANGLE: AN OPTION FOR ASSESSING PATELLAR HEIGHT ON PROXIMAL TIBIA OSTEOTOMY

OBJECTIVE

To compare the plateau-patella angle method to the methods already established for patellar height measurement in patients undergoing high tibial osteotomy.

METHODS

This is a retrospective study of 13 patients undergoing medial opening tibial osteotomy. The patellar height was measured in pre and post-operative radiographs by the methods from Insall-Salvati, Caton-Deschamps, Blackburne-Peel and patella-plateau angle, as well as the tibial slope and length of the patellar tendon. Measurements were performed by two knee surgeons at two different times.

RESULTS

The mean age was 41.33 ± 01.09 years old. The average rates of Caton-Deschamps, Blackburne-Peel, Insall-Salvati and plateau-patella angle were, respectively, 1.00; 0.89; 1.10; and 23.15° preoperatively, and 0.89; 0.78; 1.11; and 20.46°, postoperatively. The correlation of Caton-Deschamps, Blackburne-Pell, and Insall-Salvati indexes and plateau-patellar angle interobserver was 0.72 (p <0.001), 0:54 (p <0.001), 0.65 (p <0.001), and 0.67 (w <0.001), respectively.

CONCLUSION

The plateau-patella angle method undergoes changes that are correlated with changes in tibial slope after osteotomy, unlike the classical methods. This fact may lead to overestimate the reduction of patellar height after osteotomy. Level of evidence IV. Case Series.

Reconstruction of the medial patellofemoral ligament by means of the anatomical double-bundle technique using metal anchors

Objective

To evaluate double-bundle reconstruction of the medial patellofemoral ligament (MPFL) using a graft from the semitendinosus tendon and fixation with metal anchors over the medium term.

Methods

This was a prospective cross-sectional study. After approval from the research ethics committee, 31 patients with patellofemoral instability who underwent MPFL reconstruction by means of the anatomical double-bundle technique, with fixation using metal anchors, were analyzed between May 2010 and January 2015. To evaluate the effectiveness of the MPFL reconstruction surgery, the Kujala scale and the Tegner–Lysholm score were assessed before the procedure and one year afterwards, along with clinical data such as pain levels, range of motion and J sign. The data were tabulated in the Excel^® software and were analyzed using the SPSS Statistics^® software, version 21. The statistical analysis was performed using the Wilcoxon T test and the McNemar test.

Results

The mean preoperative score from the Kujala test was 45.64 ± 1.24 and the postoperative score was 94.03 ± 0.79 (p < 0.001). The preoperative Tegner–Lysholm score was 40.51 ± 1.61 and the postoperative score was 91.64 ± 0.79 (p < 0.001). The preoperative range of motion was 125.96 ± 2.11 and the postoperative range was 138.38 ± 1.49 (p < 0.05).

Conclusion

MPFL reconstruction by means of the anatomical double-bundle technique is easily reproducible, without episodes of recurrence, with satisfactory results regarding restoration of stability and function of the patellofemoral joint.

Tibial tubercle osteotomy for patello-femoral joint disorders

Tibial tubercle osteotomy has a long history in the management of patella instability and patello-femoral arthritis. This review aims to provide a comprehensive review of the literature describing the biomechanics of the patello-femoral joint and the rationale behind the use of the tibial tubercle osteotomy in modern day practice. Several different tibial tubercle osteotomies are available and we aim to detail the concepts behind their use and the subsequent clinical results. With continued developments of chondrocyte implantation techniques, the potential to fill defects on the chondral surface of either the patella or trochlea in conjunction with a tibial tubercle osteotomy may well become more commonplace in a group that is commonly young and difficult to manage. Level of evidence III.

Unique patellofemoral alignment in a patient with a symptomatic bipartite patella

BACKGROUND

A symptomatic bipartite patella is rarely seen in athletic adolescents or young adults in daily clinical practice. To date, only a limited number of studies have focused on patellofemoral alignment. The current study revealed a unique patellofemoral alignment in a patient with a symptomatic bipartite patella.

METHODS

Twelve patients with 12 symptomatic bipartite patellae who underwent arthroscopic vastus lateralis release (VLR) were investigated (10 males and two females, age: 15.7±4.4years). The radiographic data of contralateral intact and affected knees were reviewed retrospectively. From the lateral- and skyline-view imaging, the following parameters were measured: the congruence angle (CA), the lateral patellofemoral angle (LPA), and the Caton-Deschamps index (CDI). As an additional parameter, the bipartite fragment angle (BFA) was evaluated against the main part of the patella in the skyline view.

RESULTS

Compared with the contralateral side, the affected patellae were significantly medialized and laterally tilted (CA: P=0.019; LPA: P=0.016), although there was no significant difference in CDI (P=0.877). This patellar malalignment was found to significantly change after VLR (CA: P=0.001; LPA: P=0.003) and the patellar height was significantly lower than in the preoperative condition (P=0.016). In addition, the BFA significantly shifted to a higher degree after operation (P=0.001).

CONCLUSIONS

Patients with symptomatic bipartite patellae presented significantly medialized and laterally tilted patellae compared with the contralateral intact side. This malalignment was corrected by VLR, and the alignment of the bipartite fragment was also significantly changed.

LEVEL OF EVIDENCE

Level IV, case series.

ASSESSMENT OF PATELLAR HEIGHT MEASUREMENT METHODS FROM DIGITAL RADIOGRAPHY

Objective: To analyze the most common methods for measuring patellar height and the impact of observer experience in correlations with the other observers using digital radiography. Methods: Sixty digital radiographs of the knee in lateral view were analyzed by four observers: a physician in the second year of medical residence in orthopedics (R2); a physician in the third year of medical residence in orthopedics (R3); an orthopedic surgeon who was a specialist in knee surgery (SK); and a radiologist who was a specialist in musculoskeletal radiology (SR). The indices used were: Insall-Salvati (IS), Blackburne-Peel (BP), Caton-Deschamps (CD) and modified Insall-Salvati (ISM). The interobserver agreement was calculated using the kappa coefficient (κ). Results: The highest correlation coefficients were found when using the IS method followed by the CD method. The worst correlation was observed in the ISM method. The highest interobserver agreement was found between the orthopedic surgeon specializing in knee surgery and the radiologist specializing in musculoskeletal radiology, for the four measurement methods used. Conclusion: Using digital radiography, the Insall-Salvati and Caton-Deschamps indexes presented the highest interobserver agreement, and this was also positively influenced by the observer's level of experience.

Effect of patient position on measurement of patellar height ratio

BACKGROUND

Patient position is an important factor which can affect the accuracy of patellar height ratio measurement. Varying degree of knee flexion angles and action of quadriceps muscle while supine or standing positions are the most concerning factors.

METHODS

Forty healthy subjects had radiographs taken of their knees at 0°, 30°, and 60° of flexion in the supine (non-weight-bearing) and standing (weight-bearing) positions. Patellar height was assessed by five different measurement methods including Insall-Salvati (IS), Modified Insall-Salvati (MIS), Caton-Deschamps (CD), Blackburne-Peel (BP), and Knee triangular ratio (KT).

RESULTS

The mean and standard deviation (SD) in the supine/standing position of each method were IS 1.0 (0.1)/1.05 (0.1), MIS 1.6 (0.2)/1.8 (0.3), CD 1.0 (0.2)/1.2 (0.2), BP 0.9 (0.2)/1.0(0.2), and KT 1(0.1)/1(0.1). Significant differences were found between supine and standing positions using all of the methods except for KT ratio. Comparisons between the various knee flexion angles were found to be statistically significant by most of the measurement methods, although the differences between the means were less than their SD.

CONCLUSION

Quadriceps action had a significant influence on the mean values obtained by the MIS, CD, and BP methods. In clinical practice, interpretation for patella alta or patella baja of these measurement methods should be normalized according to the patient position. Varying the degree of knee flexion did not produce clinically important effects in any of the five patellar height measurement methods.

Patellofemoral osteoarthritis after Insall's proximal realignment for recurrent patellar dislocation

PURPOSE

The aim of the present study was to retrospectively investigate the development of patellofemoral osteoarthritis after the historical Insall's proximal realignment for patellar stabilisation in patients with recurrent patellar dislocation. Furthermore, risk factors for recurrent patellar dislocation and for patellofemoral osteoarthritis development were evaluated.

METHODS

Forty-two patients underwent patellofemoral stabilising surgery by the historic Insall's proximal realignment; they were evaluated with a mean follow-up period of 52 months. Plain radiography was used to document osteoarthritic changes by using the Iwano classification. MRIs obtained at the latest follow-up were evaluated for patellofemoral cartilage lesions. Univariate and multivariate logistic regression analyses were performed to evaluate the influence of trochlear dysplasia, tibial tubercle-trochlear groove distance and patellar height on redislocation. Pearson's χ (2) and the Spearman's correlation tests were used to assess a possible correlation between trochlear dysplasia and patellar dislocation, as well as between instability and development of patellofemoral osteoarthritis.

RESULTS

At the latest follow-up, plain radiographs showed a significant increase in patellofemoral osteoarthritis (grades II-IV according to the Iwano classification) in 18 patients (43%) compared with 4 patients (10%) at the time of surgery (P = 0.001). Patellofemoral cartilage lesions (grades II-IV) were detected in 18 patients (43 %) on MRI. Nine patients (21%) had at least one incidence of redislocation at follow-up. Estimated redislocation-associated risk factors could not be determined. Trochlear dysplasia had a significant impact on patellofemoral osteoarthritis development (P = 0.001), whereas recurrent patellar instability had none (n.s.).

CONCLUSION

Insall's proximal realignment technique leads to a significant progression of patellofemoral osteoarthritis. No risk factors for redislocation could be found; however, the presence of trochlear dysplasia did correlate with patellofemoral osteoarthritis.

LEVEL OF EVIDENCE

IV.

Medial patellofemoral ligament reconstruction as an isolated or combined procedure for recurrent patellar instability

PURPOSE

The principal aim of this study was to report the outcomes of medial patellofemoral ligament (MPFL) reconstruction, used as either an isolated procedure or in combination with another stabilization procedure, for the primary treatment of recurrent patellar instability.

METHODS

Between 2007 and 2012, 45 patients with recurrent patellar instability and no prior stabilization surgery had an MPFL reconstruction by a single surgeon, either as an isolated procedure or in combination with another stabilization procedure. Questionnaires detailing patellar instability since surgery, knee pain, ability to negotiate stairs, and sports participation were completed, and data regarding examination and radiological findings were collected from the medical record.

RESULTS

A total of 36 (80%) patients completed the questionnaire at a mean of 3.1 years (minimum 1 year), whilst a further 11% had clinical follow-up of greater than 1 year. Four patients were excluded due to lack of adequate follow-up. Thirty-one patients had an isolated MPFL reconstruction and none had further patellar instability. Of the ten patients who had a combined procedure, one experienced recurrent instability. Return to sport rates were 81 and 57% for the isolated and combined groups, respectively, with the majority returning to strenuous sport (81 and 57%, respectively). Most patients (96 and 80%) could negotiate stairs without difficulty, whilst 38 and 40% reported some degree of anterior knee pain.

CONCLUSIONS

This study shows that satisfactory results can be obtained using MPFL reconstruction either in isolation or in combination to treat recurrent patellar instability. Whether the indications for an isolated MPFL can be extended further remains unclear.

LEVEL OF EVIDENCE

III.

A new reference line in diagnosing a high-riding patella on routine digital lateral radiographs of the knee

OBJECTIVE

To propose a new reference line in diagnosing a high-riding patella (patella alta) on routine digital lateral radiographs of the knee.

MATERIALS AND METHODS

On 64 routine digital lateral radiographs of adult knees with no bone pathology or surgery and over the range of knee flexion between 1.6° and 79.1° (34.4°± 16.6°), the long axis of the superimposed egg-shaped femoral condyles was drawn and moved upward to pass through the point where the posterior contours of the femoral diaphysis and the femoral condyles meet-the posterior reference point-to become a new reference line. Any part of the patella crossing the new reference line indicated a high-riding patella. The new reference line was compared with the four most common patellar height ratios (Insall-Salvati, Grelsamer-Meadows or the modified Insall-Salvati, Caton Deschamps, and Blackburne-Peel) for the drawing time, accuracy, and reproducibility (intra- and interobserver agreement).

RESULTS

The new reference line required approximately one-third to one-half of the drawing time compared to the most common patellar height ratios, with equal accuracy and complete reproducibility. On the contrary, the reproducibility of the most common patellar height ratios ranged from poor to moderate, with the best results for the Insall-Salvati ratio.

CONCLUSIONS

The new reference line proved to be a very simple, accurate, and reproducible tool in diagnosing a high-riding patella. We believe that our preliminary results are an encouraging impetus to more complex research.

Plateau-patella angle in evaluation of patellar height after total knee arthroplasty

The plateau-patella angle (PPA) has been proposed as a new and simpler method to describe patellar height. This method has not been used or validated in knees following total knee arthroplasty (TKA). A modified PPA (mPPA) was developed for use in this population. The method was validated by determining the interobserver and intraobserver reliability of the technique in 50 consecutive patients compared to three well-described methods of describing patellar height after TKA. Three observers then evaluated the mPPA of 297 post-operative radiographs to describe a normal range after TKA for a given technique and implant. The interobserver reliability was the highest for the mPPA compared to the other methods. The mean mPPA for the entire cohort was 21.06, 20.49, and 19.94 for the three observers. The modified plateau-patella angle is a reliable way to evaluate patellar height in patients who have undergone total knee arthroplasty.

Plateau-patella angle in evaluation of patellar height in osteoarthritis

BACKGROUND

The plateau-patella angle (PPA), recently introduced as a new and simpler method of measuring patellar height from the lateral radiograph, has the advantage of simplicity over previously described methods as it involves a single angular measurement without the need for calculations. The purpose of this study was to validate the use of the PPA as a measurement for patellar height in knees with moderate to severe osteoarthritis.

METHODS

A total of 331 patients who underwent total knee arthroplasty at our institution with radiographs prior to surgery were evaluated. Of those, 297 (89.2%) were felt to be adequate for review. Three observers with different levels of orthopedic training measured PPA, Insall-Salvati, Caton-Deschamps, and Blackburne-Peel indices on a subset of 50 consecutive patients. Interobserver agreement for each of the four measurements was calculated and correlation between each of the measurements within each observer was calculated. The measurement of the PPA was repeated. Intraobserver agreement for the PPA was determined and a normal range and distribution was defined for this population.

RESULTS

For the three observers, the mean PPA for the entire cohort was 25.55, 25.31, and 24.42. The intraclass correlation coefficient (ICC) was 0.81, The ICC and intraobserver assessment were the highest for the PPA compared with the other ratios. The PPA was found to correlate most strongly with the Blackburne-Peel method.

CONCLUSIONS

The plateau-patella angle is a reliable way to evaluate patellar height in the osteoarthritic population. The measurement demonstrated a higher interobserver reliability compared with previously described methods.

LEVEL OF EVIDENCE

Retrospective Level IV.

Imaging of the patellofemoral joint

The patellofemoral (PF) joint is a complex articulation, with interplay between the osseous and soft tissue structures to maintain the balance between knee mobility and stability. Disorders of the PF joint can be a source of anterior knee pain (AKP). In this article, radiographic and magnetic resonance imaging of the PF joint are reviewed, including normal anatomy, imaging techniques, and imaging-based measurements. Common imaging findings associated with AKP are reviewed, including symptomatic normal variants, tendinopathy, apophysitis, osteoarthritis, chondromalacia patella, trochlear dysplasia, excessive lateralization of tibial tuberosity, patellar maltracking, patellar dislocation and fractures, anterior bursitis, Morel-Lavallée effusions, and fat pad edema.

Alteration of the patellar height following total knee arthroplasty

INTRODUCTION

Patellofemoral related complications after total knee arthroplasty (TKA) remain clinically relevant. The hypothesis of the present study was that the patellar height changes more than 10% of its preoperative height after TKA. Possible influences of age, gender, side and navigation system on patellar height were evaluated separately in subgroups.

MATERIALS AND METHODS

A total of 107 knees were enrolled after primary TKA. The patellar height was determined for each patient preoperatively, 1 week and 1 year postoperatively on routinely performed standing lateral view radiographs at 30° knee flexion. Insall-Salvati index (ISI), modified Insall-Salvati index (MIS) as well as Miura-Kawamura index (MKI) were determined for the whole cohort.

RESULTS

One week after TKA the ISI, MIS and MKI changed by more than 10% in 24 (22%), 33 (30%) and 54 (50%) cases, respectively. Moreover, the 1 year follow-up revealed a decrease or increase of ISI in 30 (28%), MIS in 47 (44 %) and MK in 65 (61%) knees. The frequency of patella alta, norma and baja preoperatively as well as 1 week and 1 year postoperatively were not significantly different. Significant differences of patellar height changes were not noted between the defined subgroups.

CONCLUSIONS

The present study demonstrates that TKA leads, at 1 week and 1 year follow-up, to patellar height alteration more than 10% in a significant number of knee joints. However, with the use of ISI and MIS the changes of patellar height did not exceed the defined thresholds to be classified as patella alta or baja.

Kinematic differences between gender specific and traditional knee implants

In the ongoing debate about gender-specific (GS) vs. traditional knee implants, there is limited information about patella-specific outcomes. GS femoral component features should provide better patellar tracking, but techniques have not existed previously to test this accurately. Using novel computed tomography and radiography imaging protocols, 15 GS knees were compared to 10 traditional knees, for the 6 degrees of freedom of the patellofemoral and tibiofemoral joints throughout the range of motion, plus other geometric measures and quality of life (QOL). Significant differences were found for patellar medial/lateral shift, where the patella was shifted more laterally for the GS femoral component. Neither group demonstrated patellar maltracking. There were no other significant differences in this well-functioning group.

Patellar maltracking is prevalent among patellofemoral pain subjects with patella alta: an upright, weightbearing MRI study

The purpose of this study is to determine if patellar maltracking is more prevalent among patellofemoral (PF) pain subjects with patella alta compared to subjects with normal patella height. We imaged 37 PF pain and 15 pain free subjects in an open-configuration magnetic resonance imaging scanner while they stood in a weightbearing posture. We measured patella height using the Caton-Deschamps, Blackburne-Peel, Insall-Salvati, Modified Insall-Salvati, and Patellotrochlear indices, and classified the subjects into patella alta and normal patella height groups. We measured patella tilt and bisect offset from oblique-axial plane images, and classified the subjects into maltracking and normal tracking groups. Patellar maltracking was more prevalent among PF pain subjects with patella alta compared to PF pain subjects with normal patella height (two-tailed Fisher's exact test, p<0.050). Using the Caton-Deschamps index, 67% (8/12) of PF pain subjects with patella alta were maltrackers, whereas only 16% (4/25) of PF pain subjects with normal patella height were maltrackers. Patellofemoral pain subjects classified as maltrackers displayed a greater patella height compared to the pain free and PF pain subjects classified as normal trackers (two-tailed unpaired t-tests with Bonferroni correction, p<0.017). This study adds to our understanding of PF pain in two ways-(1) we demonstrate that patellar maltracking is more prevalent in PF pain subjects with patella alta compared to subjects with normal patella height; and (2) we show greater patella height in PF pain subjects compared to pain free subjects using four indices commonly used in clinics.

Patella instability: building bridges across the ocean a historic review

The diagnosis of and treatment for musculoskeletal disease and injuries have seen an explosion of new knowledge. More precise imaging, correlative injury anatomy, more focused physical examination features, among others, have led this upsurge of current insight. Crucial to this knowledge revolution is the expansion of international knowledge, which is aided by an adoption of a universal scientific language, electronic transfer of information, and personal communication of surgeons and scientists across national boundaries. One area where this is particularly evident is in our knowledge and treatment for patellofemoral disorders. This article will review the developments in the management of patellar dislocations by tracing their historical roots. This is not meant to be a comprehensive review, but rather to give current readers a "historical memory" upon which to judge and interpret our present-day bridge of knowledge. Level of evidence V.

A Planar-Dimensions Machine Vision Measurement Method Based on Lens Distortion Correction

Lens distortion practically presents in a real optical imaging system causing nonuniform geometric distortion in the images and gives rise to additional errors in the vision measurement. In this paper, a planar-dimensions vision measurement method is proposed by improving camera calibration, in which the lens distortion is corrected on the pixel plane of image. The method can be divided into three steps: firstly, the feature points, only in the small central region of the image, are used to get a more accurate perspective projection model; secondly, rather than defining a uniform model, the smoothing spline function is used to describe the lens distortion in the measurement region of image, and two correction functions can be obtained by fitting two deviation surfaces; finally, a measurement method for planar dimensions is proposed, in which accurate magnification factor of imaging system can be obtained by using the correction functions. The effectiveness of the method is demonstrated by applying the proposed method to the test of measuring shaft diameter. Experimental data prove that the accurate planar-dimensions measurements can be performed using the proposed method even if images are deformed by lens distortion.

The radiological assessment of total and unicompartmental knee replacements

Radiological assessment of total and unicompartmental knee replacement remains an essential part of routine care and follow-up. Appreciation of the various measurements that can be identified radiologically is important. It is likely that routine plain radiographs will continue to be used, although there has been a trend towards using newer technologies such as CT, especially in a failing knee, where it provides more detailed information, albeit with a higher radiation exposure. The purpose of this paper is to outline the radiological parameters used to evaluate knee replacements, describe how these are measured or classified, and review the current literature to determine their efficacy where possible.

Multimodality correlations of patellar height measurement on X-ray, CT, and MRI

PURPOSE

To investigate whether the universally accepted range of normal patellar height ratios derived from radiography for the Insall-Salvati (IS) and Blackburne-Peel (BP) methods could be similarly applied to both CT and MRI.

MATERIALS AND METHODS

Institutional review board approval was obtained with waiver of informed consent for this HIPPA-compliant study. A total of 45 knees in 42 patients (15 men, 27 women; age range 11 to 75 years, mean age 39 ± 20 years) who underwent tri-modality (radiograph, CT, and MRI) examinations were selected. All patients had knee imaging obtained for a variety of reasons and measurements were performed by two independent readers who were blinded to each other's measurements or the respective measurements derived from each of the methods. Paired t test was used to compare the mean values among the modalities. Inter-observer and inter-method agreements were assessed using intra-class correlation coefficients.

RESULTS

Statistically significant, but small quantitative differences are noted between tri-modality patellar height ratios. For comparable results, the small addition of 0.13 and 0.10 are needed for the Insall-Salvati measurements on MRI and CT respectively, compared with radiographs. For the Blackburne-Peel ratio, an additional adjustment of 0.09 is needed between radiographs and MRI, but not between radiographs and CT. These adjustments are independent of gender. The interobserver reproducibility was excellent (ICC ≥ 0.94) for both the Insall-Salvati and Blackburne-Peel methods for all modalities.

CONCLUSION

The results indicate that cut-off values for patella alta and baja derived from radiographs should not be directly transposed to CT and MRI; however, the adjustments are relatively minor. These measurements show excellent reproducibility for all modalities currently used for patellar height measurements.

High tibial osteotomy

High tibial osteotomy (HTO) is a widely performed procedure to treat medial knee arthrosis. In general, published studies on HTO report good long-term results with a correct patient selection and a precise surgical technique. The ideal candidate for an HTO is a middle aged patient (60 to 65 years of age), with isolated medial osteoarthritis, with good range of motion and without ligamentous instability. Some issues that need resolution remain; these include the choice between opening and closing wedge tibial osteotomy, the graft selection in opening wedge osteotomies, the type of fixation, the comparison with unicompartmental knee arthroplasty and whether HTO significantly affects a subsequent total joint replacement. Precise indication, preoperative planning, and operative technique selection are essential to achieve good results.

Utility of tibial tubercle osteotomy in the setting of periprosthetic infection after total knee arthroplasty

PURPOSE

This study reports radiographic and clinical treatment outcomes of tibial tubercle osteotomy (TTO) used for two-stage revision total knee arthroplasty (TKA) in the setting of periprosthetic infection.

METHODS

Thirty-six patients with 51 TTOs used for infected TKA were retrospectively analysed from 2000 to 2010. In 15 of 36 patients, TTO was used in a sequential manner during both first and second stage procedures. The mean follow-up period was 57 months (range seven-126 months).

RESULTS

The mean pre-operative range of knee motion was 40° (range 10-90°), and at latest follow-up it was 92° (range 50-140°). The Knee Society knee scores and function scores were 47 and 9 pre-operatively and 82 and 72 at latest follow-up, respectively. Bony union was achieved in all cases except one nonunion of an avulsion fragment of the osteotomy segment without functional deterioration.

CONCLUSIONS

TTO can be a useful extensile surgical approach for treatment of infected TKA with satisfactory clinical and radiographic outcomes.

The patho-anatomy of patellofemoral subluxation

Patella subluxation assessed on dynamic MRI has previously been shown to be associated with anterior knee pain. In this MRI study of 60 patients we investigated the relationship between subluxation and multiple bony, cartilaginous and soft-tissue factors that might predispose to subluxation using discriminant function analysis. Patella engagement (% of patella cartilage overlapping with trochlea cartilage) had the strongest relationship with subluxation. Patellae with > 30% engagement tended not to sublux; those with < 30% tended to sublux. Other factors that were associated with subluxation included the tibial tubercle-trochlea notch distance, vastus medialis obliquus distance from patella, patella alta, and the bony and cartilaginous sulcus angles in the superior part of the trochlea. No relationship was found between subluxation and sulcus angles for cartilage and bone in the middle and lower part of the trochlea, cartilage thicknesses and Wiberg classification of the patella. This study indicates that patella engagement is a key factor associated with patellar subluxation. This suggests that in patients with anterior knee pain with subluxation, resistant to conservative management, surgery directed towards improving patella engagement should be considered. A clinical trial is necessary to test this hypothesis.

The role of high tibial osteotomy in the varus knee

High tibial osteotomy (HTO) is a widely performed procedure, and good results can be achieved with appropriate patient selection and precise surgical technique. Clinical indications include varus alignment of the knee associated with medial compartment arthrosis, knee instability, medial compartment overload following meniscectomy, and osteochondral defects requiring resurfacing procedures. Coronal alignment (ie, varus, valgus) and sagittal alignment (ie, tibial slope) should be thoroughly evaluated in all cases. Many techniques have been described for HTO, whether alone or in combination with other procedures (eg, anterior cruciate ligament reconstruction, meniscal transplant, cartilage resurfacing). Little direct evidence exists regarding the effectiveness of HTO alone or in combination with other procedures because of the lack of randomized controlled studies. However, it is commonly accepted that correct alignment is essential in achieving durable results.