Biomechanics of the patello-femoral joint. Part II: A study of the effect of simulated femoro-tibial varus deformity on the congruity of the patello-femoral compartment and movement of the patella

Cartilage degeneration is associated with activation of the PI3K/AKT signaling pathway in a growing rat experimental model of developmental trochlear dysplasia

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Established a new experimental rat model of the developmental trochlear dysplasia;

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Using the macroscopic morphological and micro-CT to assess trochlear dysplasia;

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Using Histological staining to investigate the cartilage degradation of the model;

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Investigated the relationship of the PI3K/AKT signaling pathway with trochlear dysplasia cartilage degeneration;

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Using immunohistochemistry and qPCR to investigate the PI3K/AKT and the marker of the cartilage degeneration.

Introduction

Trochlear dysplasia is a commonly encountered lower extremity deformity in humans. However, the molecular mechanism of cartilage degeneration in trochlear dysplasia is unclear thus far.

Objectives

The PI3K/AKT signaling pathway is known to be important for regulating the pathophysiology of cartilage degeneration. The aim of this study was to investigate the relationship of the PI3K/AKT signaling pathway with trochlear dysplasia cartilage degeneration.

Methods

In total, 120 female Sprague-Dawley rats (4 weeks of age) were randomly separated into control and experimental groups. Distal femurs were isolated from the experimental group at 4, 8, and 12 weeks after surgery; they were isolated from the control group at the same time points. Micro-computed tomography and histological examination were performed to investigate trochlear anatomy and changes in trochlear cartilage. Subsequently, expression patterns of PI3K/AKT, TGFβ1, and ADAMTS-4 in cartilage were investigated by immunohistochemistry and quantitative polymerase chain reaction.

Results

In the experimental group, the trochlear dysplasia model was successfully established at 8 weeks after surgery. Moreover, cartilage degeneration was observed beginning at 8 weeks after surgery, with higher protein and mRNA expression levels of PI3K/AKT, TGFβ1, and ADAMTS-4, relative to the control group.

Conclusion

Patellar instability might lead to trochlear dysplasia in growing rats. Moreover, trochlear dysplasia may cause patellofemoral osteoarthritis; cartilage degeneration in trochlear dysplasia might be associated with activation of the PI3K/AKT signaling pathway. These results provide insights regarding the high incidence of osteoarthritis in patients with trochlear dysplasia. However, more research is needed to clarify the underlying mechanisms.

Rehabilitation Variability Following Femoral Condyle and Patellofemoral Microfracture Surgery of the Knee

OBJECTIVE

To assess the variability of postoperative rehabilitation protocols used by orthopedic surgery residency programs for microfracture of femoral condyle and patellofemoral lesions of the knee.

DESIGN

Online postoperative microfracture rehabilitation protocols from US orthopedic programs and the scientific literature were reviewed. A custom scoring rubric was developed to analyze each protocol for the presence of discrete rehabilitation modalities and the timing of each intervention.

RESULTS

A total of 18 programs (11.6%) from 155 US academic orthopedic programs' published online protocols and a total of 44 protocols were analyzed. Seventeen protocols (56.7%) recommended immediate postoperative bracing for femoral condyle lesions and 17 (89.5%) recommended immediate postoperative bracing for patellofemoral lesions. The average time to permitting weight-bearing as tolerated (WBAT) was 6.1 weeks (range, 0-8) for femoral condyle lesions and 3.7 weeks (range, 0-8 weeks) for patellofemoral lesions. There was considerable variation in the inclusion and timing of strength, proprioception, agility, and pivoting exercises. For femoral condyle lesions, 10 protocols (33.3%) recommended functional testing prior to return to sport at an average of 23.3 weeks postoperatively (range, 12-32 weeks). For patellofemoral lesions, 4 protocols (20.0%) recommended functional testing for return to sport at an average of 21.0 weeks postoperatively (range, 12-32 weeks).

CONCLUSION

A minority of US academic orthopedic programs publish microfracture rehabilitation protocols online. Among the protocols currently available, there is significant variability in the inclusion of specific rehabilitation components and timing of many modalities. Evidence-based standardization of elements of postoperative rehabilitation may help improve patient care and subsequent outcomes.

Analyses of the neandertal patellae from El Sidrón (Asturias, Spain) with implications for the evolution of body form in Homo

The evolution of the body form in Homo and its potential morphological connection to the arrangement of different skeletal systems is of major interest in human evolution. Patella morphology as part of the knee is potentially influenced by body form. Here, we describe for the first time the patellae remains recovered at El Sidrón Neandertal site and analyze them in a comparative evolutionary framework. We aim to clarify whether morphometric features frequently observed in Neandertal and modern human patellae are retained from a primitive anatomical arrangement or whether they represent derived features (apomorphies). For this purpose, we combine analyses of discrete features, classic anthropological measurements, and 3D geometric morphometrics based on generalized Procrustes analysis, mean size and shape comparisons, and principal components analysis. We found a size increment of the patella in hominin evolution, with large species showing a larger patella. Modern humans and Neandertals exhibit overall larger patellae, with maximum values observed in the latter, likely as a consequence of their broader body shape. Also, some Neandertals display a thicker patella, which has been linked to larger quadriceps muscles. However, Neandertals retain a primitive morphology in their patellar articular surfaces, with similar-sized lateral and medial articular facets, leading to a more symmetrical internal face. This feature is inherited from a primitive Homo ancestor and suggests a different configuration of the knee in Neandertals. Conversely, Homo sapiens exhibits an autoapomorphic patellar anatomy with expanded lateral articular facets. We propose that these distinct configurations of the patella within Homo may be a consequence of different body forms rather than specific functional adaptations of the knee. Thus, the slender body form of modern humans may entail a medial reorientation of the tibial tuberosity (patellar ligament), allowing lateral surface expansion. These anatomical evolutionary variations may involve subtle secondary differences in bipedalism within Homo.

Significant influence of rotational limb alignment parameters on patellar kinematics: an in vitro study

PURPOSE

Component malrotation has a major impact on patellar kinematics in total knee arthroplasty. The influence of natural rotational limb alignment on patellar kinematics is unclear so far. Based on recent clinical investigations, we hypothesized that rotational limb alignment significantly influences patellar kinematics.

METHODS

Patellar kinematics of ten cadaveric knees was measured using computer navigation during passive motion. Data were correlated with different rotational limb alignment parameters of preoperative CT scans.

RESULTS

Femoral antetorsion showed a significant influence on patellar rotation, while tibial tubercle-posterior cruciate ligament distance additionally displayed a significant influence on patellar mediolateral shift (p < 0.05). Femoral posterior condylar angle was sensitive to patellar epicondylar distance, rotation and tilt (p < 0.05). Patellar rotation was influenced by five out of eight rotational limb alignment parameters (p < 0.05).

CONCLUSIONS

Rotational limb alignment should be paid more attention in terms of clinical evaluation of patellar tracking and future biomechanical and clinical investigations.

Femoral trochlear dysplasia after patellar dislocation in rabbits

BACKGROUND

The aim of this study was to investigate the effects of patellar dislocation on the development of the trochlear groove in rabbits.

METHODS

Eighty knees from forty one-month-old white rabbits were divided into three groups (sham surgery, experimental, control). Lateral patellar dislocation was established in the experimental group and the effect on the development of the trochlear groove was compared with that in the sham surgery and control groups. Computed tomography (CT) scans were conducted to measure the angle, width and depth of the trochlear groove one month and six months after surgery. Gross specimen examination, cross-sectional anatomy and histological observation were conducted to investigate the anatomical configuration of the femoral trochlea and the changes in cartilage tissue of the trochlear groove at six months after surgery.

RESULTS

At six months after surgery, CT scans showed a significant difference between the sham surgery group and the experimental group in the angle, width and depth of the trochlear groove. There were no significant differences between the sham surgery group and the control group. Gross specimen examination and cross-sectional anatomy indicated low lateral femoral trochlea and reduced height at the trochlear groove in the experimental group. The femoral trochlea was of normal appearance in the other two groups. Histological investigations showed that there were degenerative changes in the cartilage tissue of the femoral trochlea in the experimental group.

CONCLUSIONS

Secondary femoral trochlear dysplasia may be caused by patellar dislocation in a normally developing femoral trochlea. Patellar dislocation may be one of the causes of femoral trochlear dysplasia.

Development of the femoral trochlear groove in rabbits with patellar malposition

PURPOSE

The geometry of the trochlear groove is considered to be an important determinant in the pathogenesis of the patellofemoral joint disorders. However, the effect of patellar position during the development of the femoral trochlear groove is unclear. This animal study aimed to investigate the relationship between the position of the patella and development of the femoral trochlear groove in growing rabbits.

METHODS

Thirty-two knees from 16 rabbits were included in this study and were divided into two groups. First group consisted of the left knees and was used as a control group with no surgical interventions. The second group involved the right knees on which patellar tendon Z-plasty lengthening was performed to cause patellar malposition (patella alta) before 1 month of age. Computed tomographic (CT) evaluations of both knees were obtained when the animals were 1 month age before the surgical intervention and also at 6 months after the surgical intervention. Angle and depth measurements were acquired from the proximal, middle, and distal reference points along the femoral trochlear groove. After the CT scan acquisition at 6 months following the surgical procedures, rabbits were killed and additional measurements of the trochlear groove angles were performed manually.

RESULTS

The mean middle and distal trochlear groove angles for the experiment group with patella alta were significantly higher compared to that of control group (p < 0.017). The increase in mean trochlear depth for the animals in the control group was found to be significantly higher compared to experiment group at the distal zone (p < 0.017).

CONCLUSION

Distal femoral groove with an inadequately positioned patella becomes more flattened and this may be a predisposing factor for patellar instability.

LEVEL OF EVIDENCE

Controlled laboratory study, Level II.

Development of femoral trochlear groove in growing rabbit after patellar instability

PURPOSE

The geometry of an articular surface is an important determinant of joint function. Although the geometry of the trochlear groove is considered to be important in the pathogenesis of patellofemoral joint disorders, the effects of the patella during the development of the femoral trochlear groove are unclear. This animal study aimed to investigate the relationship between the position of the patella and development of femoral trochlear groove in growing rabbits.

METHODS

Twenty-four knees of 12 rabbits were included in this study and were divided into two groups. First group consisted of the left knees and was used as the control group to which no surgical procedures were applied. Second group involved the right knees to which medial soft tissue restraints release was applied before 1 month of age. Computed tomographic (CT) evaluation of both knees of each rabbit was made in their first month of age before medial retinacular release and also during post-op 1-year follow-up. CT measurements included both the angle and depth of the femoral trochlear groove from 3 different parts (proximal, middle and distal) of the distal femur, and then these measurements were averaged.

RESULTS

Measurements revealed that while in the control group the groove angle decreased 27.4 degrees and the depth increased 0.11 mm, in the operated counterparts groove angle decreased 16.8 degrees and groove depth increased 0.03 mm, which indicated the flattening of the femoral groove in the operated group. These differences were found to be statistically significant (P < 0.05).

CONCLUSION

The results indicated that distal femoral groove with inadequate patellar position becomes more flattened and causes predisposition for patellar instability. Consequently, the clinical relevance of this study was that early reconstruction of the patellofemoral joint should be performed in the childhood to prevent the patellofemoral problems that are likely to be encountered in the following years.

A randomized trial of patellofemoral bracing for treatment of patellofemoral osteoarthritis

PURPOSE

The number of effective knee osteoarthritis (OA) interventions, especially those tailored to specific compartmental involvement, are small. The objective of this study was to determine the efficacy of a realigning patellofemoral (PF) brace in improving pain and function among persons with symptomatic lateral PF OA.

METHOD

We conducted a double blind, randomized crossover trial of a realigning PF brace for persons with lateral PF OA. Participants had lateral PF OA with anterior knee symptoms on most days of the month, lateral PF joint space narrowing, and radiographic evidence of a definite osteophyte in the PF joint. We compared two treatments: (1) Control treatment consisting of a BioSkin Q Brace with patellar realigning strap removed; and (2) Active treatment consisting of a realigning BioSkin Q Brace with the strap applied. For each participant, the trial lasted 18 weeks, including 6 weeks each of active and control treatment period separated by a 6-week washout period. The order of treatments was randomized. The primary outcome was change in knee pain on the visual analog scale (VAS). Secondary outcomes included WOMAC pain, function, and stiffness. An unstructured correlation matrix for observations within participants was used in generalized estimating equation fitting to derive a linear regression model that expressed the relation between the intervention and change in VAS pain.

RESULTS

80 participants (63 F) with a mean age and body mass index of 61 years and 28 kg/m(2), respectively, were randomized by order of treatment. A model examining the main effects for change in VAS knee pain (0-100) demonstrated no significant treatment effect (-0.68 VAS units, 95% CI: -6.2, 4.8 units, P=0.81) and no differential carryover effect. There was also no significant difference between active and control treatments for WOMAC pain, function, or stiffness outcomes.

CONCLUSION

The effects of a specific realigning PF brace are not of clinical or statistical significance.

The association between patellar alignment on magnetic resonance imaging and radiographic manifestations of knee osteoarthritis

The aim of our study was to evaluate the association between patellar alignment by using magnetic resonance imaging images and radiographic manifestations of patello-femoral osteoarthritis (OA). Subjects were recruited to participate in a natural history study of symptomatic knee OA. We examined the relation of patellar alignment in the sagittal plane (patellar length ratio (PLR)) and the transverse plane (sulcus angle (SA), lateral patellar tilt angle (LPTA), and bisect offset (BO)) to radiographic features of patello-femoral OA, namely joint space narrowing and patellar osteophytes, using a proportional odds logistic regression model while adjusting for age, sex, and bone mass index (BMI). The study sample consisted of 126 males (average age 68.0 years, BMI 31.2) and 87 females (average age 64.7 years, BMI 31.6), 75% of whom had tibiofemoral OA (a Kellgren-Lawrence score of 2 or more). PLR showed a statistically significant association with joint space narrowing and osteophytosis in the lateral compartment. SA showed significant association with medial joint space narrowing and with lateral and medial patellar osteophytosis. LPTA and BO showed significant association with both radiographic indices of the lateral compartment. Clear linear trends were found in association between PLR, LPTA and BO, and with outcomes associated with lateral patello-femoral OA. SA, LPTA, and BO showed linear trends of association with medial joint space narrowing. Results of our study clearly suggest the association between indices of patellar alignment and such features of patello-femoral OA as osteophytosis and joint space narrowing. Additional studies will be required to establish the normal and abnormal ranges of patellar alignment indices and their longitudinal relation to patello-femoral OA.

The association between patella alignment and knee pain and function: an MRI study in persons with symptomatic knee osteoarthritis

OBJECTIVE

The aim of the study was to examine the association between patellofemoral (PF) alignment (using standard magnetic resonance imaging (MRI) images of extended knees) and knee pain and function.

DESIGN

Subjects were recruited to participate in a natural history study of symptomatic knee osteoarthritis, called the Boston Osteoarthritis of the Knee Study (BOKS). The association of predictive variable (patellar alignment in sagittal and transverse planes) and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain and function were examined using a linear regression model while adjusting for age, sex, body mass index (BMI), Center for Epidemiologic Studies Depression Scale (CES-D) score and Kellgren and Lawrence score.

RESULTS

Increasing trochlear angle (TA) was associated with both WOMAC (P=0.06) pain and WOMAC function subscale (P=0.04). Increasing lateral patellar title angle (LPTA) and decreasing bisect offset (increasing lateral subluxation) appeared to be associated with increasing WOMAC pain. However, no such an association was observed for other predictors.

CONCLUSIONS

The findings of the present study suggest that increasing TA is associated with increased functional impairment. Other measures of PF malalignment were not significantly associated with either knee pain or functional impairment.

Patella malalignment, pain and patellofemoral progression: the Health ABC Study

OBJECTIVE

Patellofemoral (PF) joint osteoarthritis (OA) is strongly correlated with lower extremity disability and knee pain. Risk factors for pain and structural progression in PF OA are poorly understood. Our objective was to determine the association between patella malalignment and its relation to pain severity, and PF OA disease progression.

METHODS

We conducted an analysis of data from the Health ABC knee OA study. Health ABC is a community based, multi-center cohort study of 3075 Caucasian and Black men and women aged 70-79 at enrollment. Weight bearing skyline knee X-rays were obtained in a subset (595) of subjects, with and without knee pain, at year 2 and year 5 (mean follow-up 36 months). Films were read paired, and PF osteophytes (OST) and joint space narrowing (JSN) were scored on a 0-3 scale using the Osteoarthritis Research Society International atlas. We defined progression of PF OA as any increase in JSN score. Three measures of patella malalignment were made: sulcus angle; patella tilt angle; and patella subluxation medially or laterally (bisect offset). Knee symptoms were assessed using a knee specific Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) knee pain subscale. We assessed the relationship between baseline patella malalignment and pain severity (linear regression for WOMAC) and compartment specific PF OA progression (logistic regression for dichotomous outcomes). We classified continuous measures of patella alignment into quartile groups. We performed multivariable adjusted logistic regression models, including age, gender and body mass index (BMI) to assess the relation of baseline patella alignment to the occurrence of PF JSN progression using generalized estimating equations (GEE).

RESULTS

The subjects had a mean age 73.6 (SD 2.9), BMI 28.8 (SD 4.9), 40.3% male, and 46% were Black. Medial displacement of the patella predisposed to medial JSN progression; odds for each quartile 1, 1.2, 1.2, 2.2 (P for trend=0.03), whilst protecting from lateral JSN progression; odds for each quartile 1, 0.7, 0.6, 0.4 (P for trend=0.0004). Increasing patella tilt protected from medial JSN progression; odds for each quartile 1, 0.8, 0.5, 0.2 (P<0.0001) and trended to increasing pain severity (P=0.09).

CONCLUSION

Patella malalignment is associated with PF disease progression. Medial displacement and tilt of the patella predisposes to medial JSN progression, whilst lateral displacement is predictive of lateral JSN progression. The influence of patella malalignment has important implications since it is potentially modifiable through footwear, taping and/or knee bracing.

Current concepts in the rehabilitation following articular cartilage repair procedures in the knee

Postoperative rehabilitation programs following articular cartilage repair procedures will vary greatly among patients and need to be individualized based on the nature of the lesion, the unique characteristics of the patient, and the type and detail of each surgical procedure. These programs are based on knowledge of the basic science, anatomy, and biomechanics of articular cartilage as well as the biological course of healing following surgery. The goal is to restore full function in each patient as quickly as possible by facilitating a healing response without overloading the healing articular cartilage. The purpose of this paper is to overview the principles of rehabilitation following articular cartilage repair procedures. Furthermore, specific rehabilitation guidelines for debridement, abrasion chondroplasty, microfracture, osteochondral autograft transplantation, and autologous chondrocyte implantation will be presented based upon our current understanding of the biological healing response postoperatively.

Collagen synthesis of articular cartilage explants in response to frequency of cyclic mechanical loading

Articular cartilage in vivo experiences the effects of both cell-regulatory proteins and mechanical forces. This study has addressed the hypothesis that the frequency of intermittently or continuously applied mechanical loads is a critical parameter in the regulation of chondrocyte collagen biosynthesis. Cyclic compressive pressure was applied intermittently to bovine articular cartilage explants by using a sinusoidal waveform of 0.1-1.0 Hz frequency with a peak stress of 0.5 MPa for a period of 5-20 s followed by a load-free period of 10-1,000 s. These loading protocols were repeated for a total duration of 6 days. In separate experiments, cyclic loading was continuously applied by using a sinusoidal waveform of 0.001-0.5 Hz frequency and a peak stress of 1.0 MPa for a period of 3 days. Unloaded cartilage discs of the same condyle were cultured in identically constructed loading chambers and served as controls. We report quantitative data showing that (1) no correlation exists between the relative rate of collagen synthesis expressed as the proportion of newly synthesized collagen among newly made proteins and either the frequency of intermittently or continuously applied loads or the overall time cartilage is actively loaded, and (2) individual protocols of intermittently applied loads can reduce the relative rate of collagen synthesis and increase the water content, whereas (3) continuously applied cyclic loads always suppress the relative rate of collagen synthesis compared with that of unloaded control specimens. The results provide further experimental evidence that collagen metabolism is difficult to manipulate by mechanical stimuli. This is physiologically important for the maintainance of the material properties of collagen in view of the heavy mechanical demands made upon it. Moreover, the unaltered or reduced collagen synthesis of cartilage explants might reflect more closely the metabolism of normal or early human osteoarthritic cartilage.

In vivo assessment of patellofemoral joint contact area in individuals who are pain free

Magnetic resonance imaging was used to quantify in vivo patellofemoral joint contact area and to determine if contact area is affected by quadriceps muscle contraction. Ten subjects without pain (six women, four men) had their right patellofemoral joint imaged. Cartilage-enhanced, axial plane images were obtained at 0 degrees, 20 degrees, 40 degrees, and 60 degrees knee flexion under quadriceps loaded (contracted) and quadriceps unloaded (relaxed) conditions. Medial and lateral facet contact area measurements were obtained on each image, and then summed across all images in a series to yield facet contact area measurements for each knee angle. Total contact area was computed as the sum of medial and lateral facet contact areas. Consistent with in vitro studies, progressive increases in patellofemoral joint contact area were observed from 0 degrees to 60 degrees knee flexion. The lateral facet comprised a greater percentage of total contact area compared with the medial facet at each knee flexion angle, suggesting increased load-bearing potential. Quadriceps contraction did not affect patellofemoral joint contact area indicating that the addition of a compressive load to the joint did not alter the area of the load-bearing surfaces. In vivo assessment of patellofemoral joint contact area could provide insight into mechanisms of patellofemoral joint disorders.

Provoked anterior knee pain in medial osteoarthritis of the knee

The incidence and the causes of provoked anterior knee pain in medial osteoarthritis (OA) of the knee were investigated clinically and radiographically. A retrospective study was performed in 179 primary osteoarthritic knees of 129 patients. Provocative tests were conducted on the patellofemoral (PF) joint to induce retropatellar crepitation, grating pain, tenderness around the patella, and pain on deviating the patella. The femorotibial angle (FTA) was measured on standing anteroposterior radiographs as a parameter of limb alignment. The widths of the medial and lateral joint space of the PF joint were measured on skyline views of standing or 30, 60 or 90 degrees knee flexion. The angle of flexion contracture was measured on lateral radiographs of knees with maximum extension. The lateral shift and tilt of the patella were measured on standing skyline views. Retropatellar crepitation was found in 70% of knees, while provoked anterior knee pain was observed in 35-45% of knees with medial OA of the knee. Standing FTA was significantly greater in knees with tenderness around the patella and pain on deviating the patella than in those without these symptoms (P<0.05). The angle of flexion contracture was significantly greater in knees with provoked symptoms in the PF joint than in those without symptoms (P<0.05). The degree of lateral shift was greater in knees with provoked symptoms (P<0.05). Flexion contracture and varus deformity of the knee with lateralization of the patella may be factors aggravating provoked PF symptoms in medial OA of the knee. The radiographic assessment in this series failed to show a significant relationship between the width of the PF joint space and the incidence of provoked PF symptoms.

Quantification of patellofemoral joint contact area using magnetic resonance imaging

To describe a method for quantifying patellofemoral joint contact area using magnetic resonance imaging (MRI), we used a repeated measures design using cadaver specimens. The use of contact area obtained from cadaveric specimens for biomechanical modeling does not permit investigators to assess the inter-subject variability in contact area as a result of patellofemoral pathology or malalignment. Therefore, a method for measuring patellofemoral joint contact area in-vivo is necessary. Six fresh frozen unmatched human cadaver knees were thawed at room temperature and minimally dissected to permit insertion of a pressure sensitive film packet into the suprapatellar pouch. A custom loading apparatus was designed to apply a compressive load to the patellofemoral joint at 30 degrees of flexion. Simultaneous measurement of contact area was made using both the pressure sensitive film technique and MRI. The intraclass correlation coefficient (ICC) and coefficient of variation were used to compare the agreement between the two methods and to assess the repeatability of the MRI method. Good agreement was found between the MRI and pressure sensitive film techniques (ICC 0.91; CV 13%). The MRI technique also was found to be highly reproducible (ICC 0.98; CV 2.3%). MRI assessment of patellofemoral joint contact area was found to be comparable to the established pressure sensitive film technique. These results suggest that this method may be a valuable tool in quantifying patellofemoral joint contact area in-vivo. Quantification of the patellofemoral joint stress has been dependent on patellofemoral joint contact area obtained from cadaver specimens, thereby negating the potential influence of subject specific variability. Developing a non-invasive technique to evaluate contact area will assist researchers and/or clinicians in obtaining patient-specific contact area data to be used in biomechanical analyses and clinical decision making.

Patellar tracking during simulated quadriceps contraction

The current study compared patella tracking during simulated concentric and eccentric quadriceps contractions in 12 knees from cadavers using a three-dimensional electromagnetic tracking system. The patella shifted (translated) and tilted medially during approximately the initial 22 degrees tibiofemoral flexion. The patella then shifted and tilted laterally for the remaining arc of tibiofemoral flexion (90 degrees). At 90 degrees tibiofemoral flexion, the patella had an orientation of lateral patella shift and lateral patella tilt. Patella shift was significantly more lateral between 40 degrees and 70 degrees tibiofemoral flexion during concentric quadriceps action than during eccentric contraction. Patella tilt was significantly more lateral between 45 degrees and 55 degrees tibiofemoral flexion during concentric quadriceps contraction than during eccentric action. No other significant differences were seen between the quadriceps contraction conditions. The current study supports the hypothesis that patellar instability is most likely a result of various anatomic and physiologic factors causing a failure of the extensor mechanism to deliver the patella into the femoral sulcus and that a patellar dislocation rarely would occur in a normal knee.

Patellofemoral joint stress during stair ascent and descent in persons with and without patellofemoral pain

OBJECTIVE

To determine if persons with patellofemoral pain (PFP) demonstrate elevated patellofemoral joint (PFJ) stress during stair ascent and descent when compared to persons without PFP.

DESIGN

A cross sectional study utilizing an experimental and a control group.

BACKGROUND

Ascending and descending stairs is one of the most painful activities of daily living for persons with PFP. Whether or not the pain associated with stair ambulation is the result of elevated joint stress (force per unit area) has not been explored.

METHODS

10 subjects with a diagnosis of PFP and 10 subjects without pain completed two phases of data collection, (1) MRI assessment to determine PFJ contact area and (2) comprehensive motion analysis during stair ambulation at self selected climbing velocities. Data obtained from both data collection sessions were utilized as input variables into a biomechanical model to quantify PFJ stress.

RESULTS

Although the knee extensor moment and PFJ reaction force (PFJRF) were significantly reduced in the PFP subjects during stair ascent, there was no difference in PFJ stress between groups. Similarly, there were no differences in PFJ stress during stair descent.

CONCLUSION

Our results do not support the hypothesis that subjects with PFP demonstrate greater joint stress during stair ascent and descent compared to subjects without pain. However, subjects with PFP appeared to maintain normal levels of PFJ stress by minimizing the PFJRF. This was accomplished through a slower cadence and a reduced knee extensor moment.

RELEVANCE

PFP is a common syndrome causing pain and functional limitations during stair climbing and other activities requiring high levels of quadriceps activity. Information obtained from this study will be useful in understanding the biomechanical mechanisms contributing to functional deficits in the PFP population.

Patellofemoral malalignment: looking beyond the viewbox

A clear understanding of the pathophysiology of anterior knee pain is inhibited by the use of imprecise, poorly defined, and often interchanged words, such as malalignment, patellar alignment, maltracking, subluxation, dislocation, and congruence. The literature is filled with articles regarding the diagnosis, "malalignment of the patella," most of which give no precise diagnosis. This article presents a definition of malalignment and a plea for rational descriptive and scientific analysis. Much of what is described is based on theory, not facts. These ideas are supported by clinical experience and logical analysis, but very little in the way of scientific data. Most of the data involve radiographic images, which present only one piece of the puzzle.

Alterations in the patella after a high tibial or distal femoral osteotomy

Knee osteotomies realign the knee in an attempt to better distribute forces across the knee. The anatomic and physiologic function of the extensor mechanism, which includes the quadriceps tendon, patella, and patella ligament, may be altered during this procedure. An understanding of these changes is important especially when additional surgery becomes necessary, such as a conversion to a total knee arthroplasty. The current authors discuss patella mechanics and changes in the patella associated with osteotomies about the knee and the influence on normal patella biomechanics. Although patella changes are uncommon after a distal femoral osteotomy, poor total knee arthroplasty outcomes after a high tibial osteotomy attributable to patella alterations exist. Surgical technique during the primary high tibial osteotomy and the conversion to the total knee arthroplasty can reliably improve the final outcome. Rigid internal fixation with early knee mobilization after high tibial osteotomy reduces the incidence of patella baja and improves total knee arthroplasty outcome after a high tibial osteotomy, whereas while patella changes after a distal femoral osteotomy are minimal and largely ignored.

Human patellar articular proportions: recent and Pleistocene patterns

The degrees of mediolateral asymmetry of the patellar articular facet, as well as the median and lateral articular angles of the facet, were compared across samples of recent humans and of Pleistocene archaic and modern fossil humans. All samples exhibit considerable variability in these patellar proportions. The articular angles are similar across the different samples, but there is a trend towards decreasing lateral angles with decreasing robusticity. The archaic humans exhibit significantly more symmetry of the medial and lateral facets than do any of the recent human samples. However, given the variability in medial versus lateral patellofemoral contact forces documented for extant humans and the roles of the distal oblique portions of vastus medialis and vastus lateralis in patellar stabilisation, it is unclear to what extent this variation in patellar articular proportions may affect knee kinesiology. The contrasts may be related to different levels of patellar stability and/or musculoskeletal hypertrophy, but they appear unlikely to have affected primary knee function.

Influence of patellar thickness on patellar tracking and patellofemoral contact characteristics after total knee arthroplasty

Although total knee arthroplasty (TKA) has become a very common procedure, patellar problems remain a major cause of disability. Patellar thickness is one of the most challenging factors. The influence of patellar thickness on patellofemoral kinematics and contact characteristics following TKA was investigated. Seven unembalmed whole-lower-extremity cadaveric specimens were used. The kinematics was measured with a magnetic tracking device (3Space Tracker System, Polhemus Navigation Sciences Division, Colchester, VT). Contact area was calculated from the kinematic data and the digitized joint surface geometrics based on a theoretical method. The patellofemoral joint contact force was measured directly using a uniaxial force transducer. Kinematically, the influence of patellar thickness on patellar flexion, rotation, and proximodistal shift was not significant. Orthopaedic surgeons are often challenged by derangement of the patellofemoral joint, especially following TKA. It is commonly assumed that restoration of overall patellar thickness is most desirable. A thin patella can reduce the contact force, but it also poses the potential risks of stress fracture and anteroposterior instability. Increasing patellar thickness might be expected to increase the effective quadriceps moment arm at low flexion angles of the knee, but potentially reduces the range of motion of the knee and predisposes to patellar subluxation. Either a thicker or a thinner patella had a smaller contact area than intact and normal-thickness patella. Therefore, the surgical technique of patellar resurfacing during TKA should attempt to reproduce the original patellar thickness.

A three-dimensional anatomical model of the human patello-femoral joint, for the determination of patello-femoral motions and contact characteristics

The object of this study is to develop a three-dimensional mathematical model of the patello-femoral joint, which is modelled as two rigid bodies representing a moving patella and a fixed femur. Two-point contact was assumed between the femur and patella at the medial and lateral sides and in the analysis, the femoral and patellar articular surfaces were mathematically represented using Coons' bicubic surface patches. Model equations include six equilibrium equations and eleven constraints: six contact conditions, four geometric compatibility conditions, and the condition of a rigid patellar ligament; the model required the solution of a system of 17 nonlinear equations in 17 unknowns, its response describing the six-degrees-of-freedom patellar motions and the forces acting on the patella. Patellar motions are described by six motion parameters representing the translations and rotations of the patella with respect to the femur. The forces acting on the patella include the medial and lateral component of patello-femoral contact and the patellar ligament force, all of which were represented as ratios to the quadriceps tendon force. The model response also includes the locations of the medial and lateral contact points on the femur and the patella. A graphical display of its response was produced in order to visualize better the motion of the components of the extensor mechanism. Model calculations show good agreement with experimental results available from the literature. The patella was found to move distally and posteriorly on the femoral condyles as the knee was flexed from full extension. Results indicate that the relative orientation of the patellar ligament with respect to the patella remains unchanged during this motion. The model also predicts a patellar flexion which always lagged knee flexion. Our calculations show that as the angle of knee flexion increased, the lateral contact point moved distally on the femur without moving significantly either medially or laterally. The medial contact point also moved distally on the femur but moved medially from full extension to about 40 degrees of knee flexion, then laterally as the knee flexion angle increased. The lateral contact point on the patella did not change significantly in the medial and lateral direction as the knee was flexed; however, this point moved proximally toward the basis of the patella with knee flexion. The medial contact point also moved proximally on the patella with knee flexion, and in a similar manner the medial contact point on the patella moved distally with flexion from full extension to about 40 degrees of flexion.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of tibial rotations on patellar tracking and patello-femoral contact areas

The object of this study is to determine the effect of tibial rotations on the three-dimensional patello-femoral motions and contact areas during a physiological loading condition, the knee-extension exercise. A commercially available device, the 3-SPACE digitizer and tracker system, was used to collect the motion data, utilizing cadaveric human lower limbs as well as the geometric measurements describing the articular surfaces at the patello-femoral joint. It was found that tibial rotations caused statistically significant differences, at the 0.05 level, in patellar tilt, patellar rotation and patellar medial-lateral shift. It was also found that while the magnitude of the total contact area at a given knee flexion angle did not change significantly with tibial rotations, medial and lateral components of the total contact areas were affected by tibial rotations. Medical femoral contact areas increased with internal tibial rotations at all flexion angles; lateral femoral contact areas increased with external tibial rotations at all flexion angles. This correlates well with the kinematic data since it was found that the patella shifted medially with internal tibial rotations at all flexion angles, and titled more medially near full-extension causing an increase in the medial contact areas and a decrease in the lateral contact areas.

Biomechanics of the patello-femoral joint. Part I: A study of the contact and the congruity of the patello-femoral compartment and movement of the patella

Techniques are described for studying the pattern of contact and congruence of the patello-femoral joint, and the movement of the patella at different angles of knee flexion. The study is carried out on cadaveric knee specimens.