Analysis of patellofemoral arthrokinematic motion quality in open and closed kinetic chains using vibroarthrography.

BACKGROUND: Knee movements performed in open (OKC) and closed (CKC) kinetic chains generate various patterns of muscle activities and especially distinct contact stresses in the patellofemoral joint (PFJ). In contrast to these features, the arthrokinematic motion quality (AMQ) of the PFJ has not been compared between mentioned conditions. In this study we performed vibroarthrographic analysis of AMQ in movements performed in OKC and CKC, in healthy subjects and individuals with chondromalacia patellae, to assess which of the test conditions is more efficient in differentiation between healthy and deteriorated joints. Moreover, our analysis will broaden the knowledge related to behavior of normal and pathological synovial joints during motion with and without weight bearing. It is an essential issue, due to the recently observed significant interest in comparing potential benefits and limitations of CKC and OKC exercises as they relate to lower extremity rehabilitation. METHODS: 100 subjects (62 healthy controls and 38 subjects with PFJ chondromalacia) were enrolled. During repeated knee flexion/extension motions performed in OKC (in a sitting position) and CKC (sit-to-stand movements), the vibroarthrographic signals were collected using an accelerometer and described by variability (VMS), amplitude (R4), and spectral power in 50-250 Hz (P1) and 250-450 Hz (P2) bands. RESULTS: Significant differences in VMS [V], R4 [V], P1 [V2/Hz] and P2 [V2/Hz] between OKC and CKC were found (0.0001, 0.969. 0.800 0.041 vs 0.013, 3.973, 6.790, 0.768, respectively, P < 0.001). Moreover, in both analyzed load-related conditions the subjects with chondromalacia were characterized by significantly higher values of all parameters, when compared to controls (P < 0.001), with effect size values over 0.6. CONCLUSIONS: We showed that motion of the physiological, unloaded PFJ articular surfaces in OKC is nearly vibrationless, which corresponds with optimal AMQ of PFJ, while loaded movements in CKC are characterized by a higher vibroacoustic emission level. Moreover, chondral lesions should be considered as an increased friction-related, aggravating factor of AMQ, which is critical in CKC movements under load. Nonetheless, OKC and CKC conditions are characterized by large effect sizes, and provide an efficient test frame for differentiating physiological knees and joints with chondral lesions.

Analysis and multiclass classification of pathological knee joints using vibroarthrographic signals.

BACKGROUND AND OBJECTIVE: Vibroarthrography (VAG) is a method developed for sensitive and objective assessment of articular function. Although the VAG method is still in development, it shows high accuracy, sensitivity and specificity when comparing results obtained from controls and the non-specific, knee-related disorder group. However, the multiclass classification remains practically unknown. Therefore the aim of this study was to extend the VAG method classification to 5 classes, according to different disorders of the patellofemoral joint. METHODS: We assessed 121 knees of patients (95 knees with grade I-III chondromalacia patellae, 26 with osteoarthritis) and 66 knees from 33 healthy controls. The vibroarthrographic signals were collected during knee flexion/extension motion using an acceleration sensor. The genetic search algorithm was chosen to select the most relevant features of the VAG signal for classification. Four different algorithms were used for classification of selected features: logistic regression with automatic attribute selection (SimpleLogistic in Weka), multilayer perceptron with sigmoid activation function (MultilayerPerceptron), John Platt's sequential minimal optimization algorithm implementation of support vector classifier (SMO) and random forest tree (RandomForest). The generalization error of classification algorithms was evaluated by stratified 10-fold cross-validation. RESULTS: We obtained levels of accuracy and AUC metrics over 90%, more than 93% sensitivity and more than 84% specificity for the logistic regression-based method (SimpleLogistic) for a 2-class classification. For the 5-class method, we obtained 69% and 90% accuracy and AUC respectively, and sensitivity and specificity over 91% and 69%. CONCLUSIONS: The results of this study confirm the high usefulness of quantitative analysis of VAG signals based on classification techniques into normal and pathological knees and as a promising tool in classifying signals of various knee joint disorders and their stages.

Patellofemoral Pain: An Enigma Explained by Homeostasis and Common Sense.

We present a rational, scientific, low-risk approach to patellofemoral pain (anterior knee pain) based on an understanding of tissue homeostasis. Loss of tissue homeostasis from overload and/or injury produces pain. Bone overload and synovial inflammation are common sources of such pain. Chondromalacia and malalignment are findings that almost always do not need to be "corrected" to relieve pain. Patience and persistence in nonoperative care results in consistent success. Surgery should be rare and done only after extensive nonoperative management and in the setting of clearly defined pathology. Rational surgical treatment is explained in the context of restoring tissue homeostasis to relieve pain.

Sagittal plane tilting deformity of the patellofemoral joint: a new concept in patients with chondromalacia patella.

PURPOSE: The aims of this study were to evaluate sagittal plane alignment in patients with chondromalacia patella via magnetic resonance imaging (MRI), analyse the relationships between the location of the patellar cartilaginous lesions and sagittal alignment and finally investigate the relationships between the sagittal plane malalignment and patellofemoral loadings using by finite element analysis. METHODS: Fifty-one patients who were diagnosed with isolated modified Outerbridge grade 3-4 patellar chondromalacia based on MRI evaluation and 51 control subjects were evaluated. Chondromalacia patella patients were divided into three subgroups according to the chondral lesion location as superior, middle and inferior. The patella-patellar tendon angle (P-PT) was used for evaluation of sagittal alignment of patellofemoral joint. Each subgroup was compared with control group by using P-PT angle. To investigate the biomechanical effects of sagittal plane malpositioning on patellofemoral joint, bone models were created at 30°, 60° and 90° knee flexion by using mean P-PT angles, which obtained from patients with chondromalacia patellae and control subjects. The total loading and contact area values of the patellofemoral joints were investigated by finite element analysis. RESULTS: The mean age of all participants was 52.9 ± 8.2 years. The mean P-PT angle was significantly lower in chondromalacia group (142.1° ± 3.6°) compared to control group (144.5° ± 5.3°) (p = 0.008). Chondral lesions were located in superior, middle and inferior zones in 16, 20 and 15 patients, respectively. The mean P-PT angles in patients with superior (141.8 ± 2.7) and inferior subgroups (139.2 ± 2.3) were significantly lower than the values in the control group (p < 0.05). The contact area values were detected higher in models with chondromalacia than in the control models at the same flexion degrees. There were increased loadings at 30° and 90° flexions in the sagittal patellar tilt models. CONCLUSION: This study revealed that sagittal plain malpositioning of the patellofemoral joint might be related to chondromalacia, especially in the presence of lesions in the upper and lower part of the patella. This condition leads to supraphysiological loadings on the patellofemoral joint. Sagittal patellar tilt should be considered in the evaluation and management of patellar cartilage defects. Taking sagittal plane malalignment into consideration in patellofemoral joint evaluation will enable us to design new physical and surgical modalities. LEVEL OF EVIDENCE: IV.

Joint motion quality in vibroacoustic signal analysis for patients with patellofemoral joint disorders.

BACKGROUND: Chondromalacia, lateral patellar compression syndrome and osteoarthritis are common patellofemoral joint disorders leading to functional and/or structural disturbances in articular surfaces. The objective of the study was to evaluate their impact on joint motion quality via the vibroacoustic signal generated during joint movement analysis. METHODS: Seventy-three patients (30 with chondromalacia, 21 with lateral patellar compression syndrome, and 22 with osteoarthritis) and 32 healthy controls were tested during flexion/extension knee motion for vibroacoustic signals using an acceleration sensor. Estimated parameters: variation of mean square (VMS), difference between mean of four maximum and mean of four minimum values (R4), power spectral density for frequency of 50-250 Hz (P1) and 250-450 Hz (P2) were analyzed. RESULTS: Vibroacoustic signals recorded for particular disorders were characterized by significantly higher values of parameters in comparison to the control group. Moreover, differences were found among the various types of patellofemoral joint disturbances. Chondromalacia and osteoarthritis groups showed differences in all parameters examined. In addition, osteoarthritis patients exhibited differences in VMS, P1 and P2 values in comparison to lateral patellar compression syndrome patients. However, only the value of R4 was found to differ between knees with lateral patellar compression syndrome and those with chondromalacia. CONCLUSION: Our results suggest that particular disorders are characterized by specific vibroacoustic patterns of waveforms as well as values of analyzed parameters.

Incidencia de las disfunciones rotatorias de la tibia en las condropatias rotulianas / Incidence of rotary disfunctions of the tibia in patellar chondropathy

Objetivos: Observar la relación entre degeneración del cartílago fémoro-rotuliano y la disfunción rotatoria tibial, en pacientes afectos de condropatía rotuliana unilateral. Material y Métodos: De una muestra de 133 sujetos se seleccionaron 50 sujetos, a los que se les aplicaron evaluaciones manuales y radiológicas (medición goniométrica en rotación tibial y radiología) para observación del posicionamiento rotuliano, mediante la medición del ángulo de congruencia y el desplazamiento transversal de la rotula. Resultados: Se observan diferencias significativas entre la rodilla afectada y la rodilla sana, tanto al comparar la rotación interna tibial, como la rotación externa tibial (p< 0,0001). En relación a la posición de la rótula, cuando se encuentra afectada la rotación interna, observamos una angulación de la rótula en sentido lateral (con respecto a la rodilla sana). Cuando está afectada la rotación externa o ambas rotaciones conjuntas, la rótula se angula hacia medial (con respecto a la rodilla sana) (p<0,02). En relación al desplazamiento lateral, no observamos resultados significativos. Conclusiones: Los procesos degenerativos del cartílago articular fémoro-rotuliano se asocian con una disfunción rotatoria tibial. Existe un sentido de angulación concreto asociado a cada tipo de afectación de rotación determinada, y tendencia a que la rótula se angule y se desplace de una manera distinta en la rodilla afecta, comparada con la rodilla sana (AU)

Objectives: To observe the relationship between degeneration of the femur-patellar cartilage and the rotating tibial dysfunction, in patients suffering from unilateral patellar chondropathy. Material and methods: From a sample of 133 subjects, 50 subjects were selected, to whom manual and radiological tests were applied (goniometric measurement in tibial and radiological rotation) for observation of patellar positioning by the measurement of the angle of congruence and lateral displacement of the patella. Results: Significant differences are observed between the affected knee and the healthy knee, both when comparing internal tibial rotation and external tibial rotation (p <0.0001). In connection with the patella position, when internal rotation is affected, we observe a lateral angulation of the patella (with regard to the healthy knee). When external rotation or both joint rotations are affected, the patella is angled inward (with respect to the healthy knee) (p <0.02). With regard to lateral displacement, we observed no significant results. Conclusions: The degenerative processes of the femur-patellar joint cartilage are associated with rotational or tibial dysfunction. There is a sense of concrete angulation associated with each type of affectation of determined rotation, and a tendency for the patella to angulate and move differently to the affected knee when compared to the healthy knee (AU)

The role of autologous chondrocyte implantation in the treatment of symptomatic chondromalacia patellae.

PURPOSE: Chondromalacia patella is a distinct clinical entity of abnormal softening of the articular cartilage of the patella, which results in chronic retropatellar pain. Its aetiology is still unclear but the process is thought to be a due to trauma to superficial chondrocytes resulting in a proteolytic enzymic breakdown of the matrix. Our aim was to assess the effectiveness of autologous chondrocyte implantation on patients with a proven symptomatic retropatellar lesion who had at least one failed conventional marrow-stimulating therapy. METHODS: We performed chondrocyte implantation on 48 patients: 25 received autologous chondrocyte implantation with a type I/III membrane (ACI-C) method (Geistlich Biomaterials, Wolhusen, Switzerland), and 23 received the Matrix-assisted Chondrocyte Implantation (MACI) technique (Genzyme, Kastrup, Denmark). RESULTS: Over a mean follow-up period of 40.3 months, there was a statistically significant improvement in subjective pain scoring using the visual analogue scale (VAS) and objective functional scores using the Modified Cincinnati Rating System (MCS) in both groups. CONCLUSIONS: Chondromalacia patellae lesions responded well to chondrocyte implantation. Better results occurred with MACI than with ACI-C. Excellent and good results were achieved in 40% of ACI-C patients and 57% of MACI patients, but success of chondrocyte implantation was greater with medial/odd-facet lesions. Given that the MACI procedure is technically easier and less time consuming, we consider it to be useful for treating patients with symptomatic chondral defects secondary to chondromalacia patellae.

Malalignment and cartilage lesions in the patellofemoral joint treated with autologous chondrocyte implantation.

PURPOSE: The aim of our current study is to present the 12.6 years' follow-up results in patients with cartilage lesions of the patellofemoral joint, treated with autologous chondrocyte implantation (ACI) with the use of periosteum. METHODS: Ninety-two patients having patella or trochlea lesion participated in this study. Lysholm and Tegner questionnaires were completed 12.6 years (SD 2.3 years) after the surgery. The patients were asked whether they feel better, worse or had not experienced any difference compared to previous years and whether they would undergo the operation again. Complications or subsequent surgeries were also assessed. RESULTS: Median Tegner score was three, improved by one level compared with preoperative values (P = 0.02). Median Lysholm score was 70, improved by nine points (n.s.). Seventy-two percent of the patients were better or unchanged while 93% would undergo the operation again. Patients with no kissing lesions appeared to have a better prognosis. Patients with malalignment or instability that had undergone a realignment procedure had comparable outcomes to the patients that did not need any additional surgery. Realignment procedures increased the incidence of serious complications but they were associated with decreased incidence of periosteal hypertrophy. No association was found between the age of the patients at the time of the ACI or the size per lesion and any of the clinical outcomes. CONCLUSION: ACI provides a satisfactory outcome for the treatment of cartilage lesions of the patellofemoral joint, even for the cases with concomitant patellar instability. It seems that correcting the coexisting background factors with realignment, stabilizing or unloading procedures, along with the treatment of cartilage lesions, is improving the clinical outcomes over time and decreases the incidence of periosteal hypertrophies although increasing the incidence of serious complications. Our study reveals the good results and the high level of patients' activities (as shown by Tegner score), were preserved 12.6 years after the implantation, in both isolated trochlea and patella lesions and also in multiple and in kissing lesions where an intervention could be considered as a salvage procedure.

[Modification of longitudinal relaxation time (T1) as a biomarker of patellar cartilage degeneration]. / Modificación del tiempo de relajación longitudinal (T1) como biomarcador de la degeneración del cartílago patelar.

OBJECTIVES: To study the viability of longitudinal relaxation time (T1) of patellar cartilage as a biomarker of the degree of degeneration. MATERIAL AND METHODS: We included 15 subjects classified into three groups according to clinical criteria (pain, functional limitation, and duration of symptoms) and imaging criteria as follows: (a) normal (3 men, 2 women; age 30+/-14 years), (b) with initial degeneration of the patellar cartilage (3 men, 2 women; age 30+/-6 years), or (c) with advanced degeneration (3 men, 2 women; age 57+/-10 years). All underwent MRI examination using special echo-gradient sequences to segment the cartilage and calculate the T1 maps. We selected the entire cartilage and the regions of interest classified according to clinical and imaging criteria as normal, initial degeneration, and advanced degeneration. The T1 values of the cartilage were obtained pixel by pixel and were calculated as the mean for the entire cartilage or by subregions (normal, initial, advanced). Differences between groups for the entire cartilage and the regions were analyzed using Student-Newman-Keuls post-hoc ANOVA. Reproducibility was evaluated using the coefficient of variance. RESULTS: No significant differences in the overall analysis of the entire cartilage were found between the three groups (normal: 1003+/-172 ms, initial: 1064+/-124 ms, advanced: 1041+/-308 ms, p=0.665). However, the analysis by regions revealed significant differences (normal: 908+/-53 ms, initial degeneration: 1057+/-157 ms, advanced degeneration: 1133+/-116 ms, p=0.029). The reproducibility analysis found variations of 1.3% for the overall calculation, 3.7% for the regional calculation, and 8.2% for the acquisition. CONCLUSION: In this preliminary study, calculating the T1 of the cartilage enabled regions with different degrees of degeneration to be differentiated.

Bone density in patients with chondromalacia patella.

Chondromalacia of the patella is the most common cause of anterior knee pain in young women. The etiology of the disease is not well-understood but the initial lesion is a disorganization of collagenous structures. Since the disease is proposed to be due to generalized constitutional disturbance, we postulated that bony structures could also be involved. To investigate this hypothesis we measured the bone density of 286 patients with the diagnosis of chondromalacia of the patella during a 4-year period using dual energy X-ray absorptiometry (DXA) method. We found a significant number of patients having low bone densities. This problem was more pronounced in men and in younger age groups. We suggest base-line bone density evaluation in all patients, treatment of osteopenia or osteoporosis in select patients and regular follow-ups using DXA.

Patellofemoral full-thickness chondral defects treated with second-generation autologous chondrocyte implantation: results at 5 years' follow-up.

BACKGROUND: Patellofemoral lesions represent a very troublesome condition to treat for orthopaedic surgeons; however, second-generation autologous chondrocyte implantation (ACI) seems to offer an interesting treatment option with satisfactory results at short-term follow-up. HYPOTHESIS: Hyaluronan-based scaffold seeded with autologous chondrocytes is a viable treatment for the damaged articular surface of the patellofemoral joint. STUDY DESIGN: Case series; Level of evidence, 4. METHODS: Among a group of 38 patients treated for full-thickness patellofemoral chondral lesions with second-generation ACI, we investigated 34 who were available for final follow-up at 5 years. These 34 had chondral lesions with a mean size of 4.45 cm(2). Twenty-one lesions were located on the patella, 9 on the trochlea, and 4 patients had multiple lesions: 3 had patellar and trochlear lesions, and 1 had patellar and lateral femoral condyle lesions. Twenty-six lesions (76.47%) were classified as International Cartilage Repair Society (ICRS) grade IV A or B, 5 lesions (14.70%) were grade IIIC, and 3 (8.82%) were lesions secondary to osteochondritis dissecans (OCD). Results were evaluated using the International Knee Documentation Committee (IKDC) 2000 subjective and objective scores, EuroQol (EQ) visual analog scale (VAS), and Tegner scores at 2 and 5 years. Eight patients had second-look arthroscopy and biopsies. RESULTS: All the scores used demonstrated a statistically significant improvement (P < .0005) at 2 and 5 years' follow-up. Objective preoperative data improved from 8 of 34 (23.52%) normal or nearly normal knees to 32 of 34 (94.12%) at 2 years and 31 of 34 (91.17%) at 5 years after transplantation. Mean subjective scores improved from 46.09 points preoperatively to 77.06 points 2 years after implantation and 70.39 at 5 years. The Tegner score improved from 2.56 to 4.94 and 4.68, and the EQ VAS improved from 56.76 to 81.47 and 78.23 at 2 and 5 years' follow-up, respectively. A significant decline of IKDC subjective and Tegner scores was found in patients with multiple and patellar lesions from 2 to 5 years' follow-up. Second-look arthroscopies in 8 cases revealed the repaired surface to be nearly normal with biopsy samples characterized as hyaline-like in appearance. CONCLUSION: Hyaluronan-based scaffold seeded with autologous chondrocytes can be a viable treatment for patellofemoral chondral lesions.

The effects of quadriceps contraction on different patellofemoral alignment subtypes: an axial computed tomography study.

STUDY DESIGN: Controlled laboratory study. BACKGROUND: The effect of quadriceps contraction on patellar alignment in patients with patellofemoral pain syndrome (PFPS) is debated and may vary based on patellar alignment subtypes measured with the quadriceps relaxed. OBJECTIVES: To determine if the effects of quadriceps contraction on patellar alignment differs (1) with respect to patellar alignment subtype in individuals with PFPS and (2) between symptomatic and asymptomatic knees in individuals with unilateral PFPS. METHODS AND MEASURES: Seventy-eight individuals, 47 with bilateral and 31 with unilateral PFPS, participated in the study. On axial computed tomography images with the knee in extension with quadriceps relaxed as well as contracted, patellar lateral condyle index (PLCI) and patellar tilt angle (PTA) were measured and analyzed. Based on the median PLCI and PTA alignment values measured with quadriceps relaxed for the 78 subjects, 4 subgroups of subjects were created: type 1, laterally displaced; type 2, laterally displaced and tilted; type 3, laterally tilted; and type 4, neither. RESULTS: Quadriceps contraction caused an increase in PLCI in all patellar alignment types (P<.01), with no difference in the magnitude of the increase between types (P>.05). PTA decreased with quadriceps contraction in the subjects with the type 3 initial patellar alignment (P<.01), with a significant difference in the change in patellar alignment between the subjects with type 3 and type 1 initial patellar alignment (P=.004). For the 31 subjects with unilateral PFPS, quadriceps contraction caused a similar change in PLCI and PTA in both the symptomatic and asymptomatic knees. CONCLUSIONS: The initial position of the patella with the quadriceps relaxed did not influence the change in PLCI with quadriceps contraction. For the 31 subjects with PFPS, there was no difference in initial alignment as well as in change of alignment with quadriceps contraction between symptomatic and asymptomatic knees.

Evaluation of magnetic resonance signal modification induced by hyaluronic acid therapy in chondromalacia patellae: a preliminary study.

Hyaluronic Acid (HA) is an alternative method for the treatment of osteoarthritis (OA), which acts on pain through a double action: anti-inflammatory and synovial fluid (SF) visco-supplementation. Magnetic Resonance Imaging (MRI), utilizing specific sequences, is a valid method for studying the initial phase of chondral damage. The analysis of the data, obtained through the intensity of values taken by positioning Region of Interest (ROIs) within the lesion, determining the differences before and after treatment with HA injected into the knee. The results obtained after six months and one year from the injection were statistically different in respect to those taken before, immediately and after three months of treatment. MRI represents a valid tool to evaluate the grade of chondromalacia patellae and also to follow the cartilage modification induced by HA therapy.

The diagnostic value of the Clarke sign in assessing chondromalacia patella.

CONTEXT: Various techniques have been described for assessing conditions that cause pain at the patellofemoral (PF) joint. The Clarke sign is one such test, but the diagnostic value of this test in assessing chondromalacia patella is unknown. OBJECTIVE: To (1) investigate the diagnostic value of the Clarke sign in assessing the presence of chondromalacia patella using arthroscopic examination of the PF joint as the "gold standard," and (2) provide a historical perspective of the Clarke sign as a clinical diagnostic test. DESIGN: Validation study. SETTING: All patients of one of the investigators who had knee pain or injuries unrelated to the patellofemoral joint and were scheduled for arthroscopic surgery were recruited for this study. PATIENTS OR OTHER PARTICIPANTS: A total of 106 otherwise healthy individuals with no history of patellofemoral pain or dysfunction volunteered. MAIN OUTCOME MEASURE(S): The Clarke sign was performed on the surgical knee by a single investigator in the clinic before surgery. A positive test was indicated by the presence of pain sufficient to prevent the patient from maintaining a quadriceps muscle contraction against manual resistance for longer than 2 seconds. The preoperative result was compared with visual evidence of chondromalacia patella during arthroscopy. RESULTS: Sensitivity was 0.39, specificity was 0.67, likelihood ratio for a positive test was 1.18, likelihood ratio for a negative test was 0.91, positive predictive value was 0.25, and negative predictive value was 0.80. CONCLUSIONS: Diagnostic validity values for the use of the Clarke sign in assessing chondromalacia patella were unsatisfactory, supporting suggestions that it has poor diagnostic value as a clinical examination technique. Additionally, an extensive search of the available literature for the Clarke sign reveals multiple problems with the test, causing significant confusion for clinicians. Therefore, the use of the Clarke sign as a routine part of a knee examination is not beneficial, and its use should be discontinued.

Retropatellar chondromalacia associated with medial osteoarthritis after meniscus injury. One year of observations in sheep.

BACKGROUND/AIMS: In an ovine meniscal repair model, the patellofemoral (PF) osteoarthritis due to a non-sutured tear or failed repair was investigated. METHODS: A radial meniscus tear was either sutured with polydioxanone (PDS), with a slow degrading polylactide long-term suture(LTS) or left without treatment. Knee joint cartilage in the PF and medial compartment was evaluated compared to normal knees (healthy controls). RESULTS: Retropatellar osteoarthritis in the non-sutured and sutured animals was intense in contrast to the control knees after 6 months in all groups (p < 0.001), and after 12 months in the PDS group (p < 0.001), LTS group and non-sutured animals (p < 0.05). CONCLUSION: Non-sutured meniscus tears and failed repair lead fast to intense PF osteoarthritis corresponding with tibial damage of the injured compartment.

In vivo study on the short-term effect of radiofrequency energy on chondromalacic patellar cartilage and its correlation with calcified cartilage pathology in an equine model.

Chondromalacia can cause joint pain and synovial effusion with the potential for developing into osteoarthritis. Thermal chondroplasty using radiofrequency energy (RFE) has been reported to be superior to mechanical debridement for treating chondromalacia. We compared short-term changes in biomechanical properties of articular cartilage after treatment with monopolar (mRFE) or bipolar RFE (bRFE) or mechanical debridement (MD) on experimentally created grade II chondromalacia patellae. Chondromalacia patellae was created arthroscopically in both patellae of 15 ponies. Ten months after surgery, each patella was randomly assigned to one of four experimental groups: sham operated, untreated control; MD; bRFE; and mRFE. Animals were euthanized 6 months after treatment and fresh osteochondral sections were collected from the treated area, the border of the chondromalacic and nonchondromalacic area, and from two untreated areas for analysis of mechanical properties. The same areas were harvested from an additional six untreated ponies. The aggregate modulus (H(A)), Poisson's ratio (nu(s)), and permeability (k) were determined for each area under creep indentation, and cartilage thickness was measured with a needle probe. The relation between zone of calcified cartilage (ZCC) and mechanical properties of hyaline cartilage (HC) was assessed histomorphometrically. Treated areas of all four groups had inferior mechanical properties compared at the same location. The treated and border areas had significantly lower H(A) values than the untreated areas. Permeability values showed significant differences between bRFE and other treated groups. Chondromalacic areas showed thinning of cartilage compared to nonchondromalacic areas. Biomechanical properties of the injured cartilage were inferior to nonchondromalacic cartilage regardless of the treatment type. mRFE had the highest stiffness value compared to other treatments and significantly higher values than MD. A significant correlation was observed between the mechanical properties of HC and ZCC thickness.

The pathophysiology of patellofemoral pain: a tissue homeostasis perspective.

UNLABELLED: Fundamental to rational, safe, and effective treatment for any orthopaedic condition is an accurate understanding of the etiology of the symptoms. The decades-old paradigm of a pure structural and biomechanical explanation for the genesis of patellofemoral pain is giving way to one in which biologic factors are being given more consideration. It is increasingly evident that a variable mosaic of possible pathophysiologic processes, often caused by simple overload, best accounts for the etiology of patellofemoral pain in most patients. Inflamed synovial lining and fat pad tissues, retinacular neuromas, increased intraosseous pressure, and increased osseous metabolic activity of the patella all have been documented as contributing to the perception of anterior knee pain. Considered together, these processes can be characterized as loss of tissue homeostasis and can be seen as providing a new and alternative explanation for the conundrum of anterior knee pain. Certain high loading conditions of the patellofemoral joint can be of sufficient magnitude to induce the symptomatic loss of tissue homeostasis so that, once initiated, they may persist indefinitely. From this new biologic perspective, it clinically matters little what structural factors may be present in a given joint (such as chondromalacia, patellar tilt or a Q angle above a certain value) if the pain free condition of tissue homeostasis is safely achieved and maintained. LEVEL OF EVIDENCE: Level V (expert opinion). See the Guidelines for Authors for a complete description of levels of evidence.