My Knee Hurts
Joseph D. Lamplot, MD
Robert H. Brophy, MD, FAAOS
Dr. Lamplot or an immediate family member serves as a paid consultant to or is an employee of DePuy, a Johnson & Johnson Company and has received research or institutional support from Arthrex, Inc. Dr. Brophy or an immediate family member serves as a board member, owner, officer, or committee member of the American Academy of Orthopaedic Surgeons, the American Orthopaedic Association, and the American Orthopaedic Society for Sports Medicine.
Introduction
Knee pain is one of the most common complaints among patients in orthopaedic clinics. Pain may result from acute trauma or from chronic degeneration of structures including the articular cartilage or meniscus. Pathologies that are frequently encountered include patellofemoral pain, meniscal tears, and ligament injuries. A thorough history and physical examination is essential in determining the etiology of the patient’s symptoms and guiding treatment. Treatment options vary depending on the pathology as well as patient-specific factors and range from nonsurgical management including activity modification, bracing, and injections to surgical management, which can include débridement, repair, reconstruction, or replacement.
PATELLOFEMORAL PAIN
Patellofemoral pain (PFP), a term that encompasses a variety of pathologies involving the patellofemoral joint, is the most common chief complaint associated with the knee and typically presents as anterior knee pain. PFP is not a diagnosis in itself, because it may
result from a variety of etiologies. Atraumatic etiologies for PFP include lateral patellar compression syndrome, chondral softening (chondromalacia patella), and patellofemoral arthritis. Traumatic etiologies include patellar instability (subluxation or dislocation), fracture, patellar or quadriceps tendinitis, and cartilage injuries of the patella or trochlea. A thorough history and physical examination is essential to determine the underlying etiology of PFP. Although an initial course of nonsurgical management is warranted in most cases of PFP, determining the cause of the patient’s symptoms is essential to formulate an appropriate treatment plan. Advanced imaging studies, typically MRI, can be helpful in making a diagnosis.
result from a variety of etiologies. Atraumatic etiologies for PFP include lateral patellar compression syndrome, chondral softening (chondromalacia patella), and patellofemoral arthritis. Traumatic etiologies include patellar instability (subluxation or dislocation), fracture, patellar or quadriceps tendinitis, and cartilage injuries of the patella or trochlea. A thorough history and physical examination is essential to determine the underlying etiology of PFP. Although an initial course of nonsurgical management is warranted in most cases of PFP, determining the cause of the patient’s symptoms is essential to formulate an appropriate treatment plan. Advanced imaging studies, typically MRI, can be helpful in making a diagnosis.
Epidemiology
PFP is the most common knee problem of patients presenting to orthopaedic clinics.
Lateral patellar compression syndrome occurs secondary to muscular imbalance (ie, vastus medialis oblique [VMO] weakness) and causes patellar maltracking and/or tilt.
Most common etiology of PFP, most often affecting adolescent females
Patellofemoral arthritis is another common cause of anterior knee pain, most commonly affecting older patients.
Chondromalacia patella (softening of the articular cartilage of the patella) occurs in younger patients and may progress to patellofemoral arthritis.
Acute chondral injuries are most common in young patients in the setting of patellar dislocations.
Commonly affect the medial facet of the patella and lateral aspect of the trochlea
Chronic chondral lesions most frequently occur secondary to overload and are typically found in female patients age 30 to 50 years.
Pertinent Anatomy/Pathoanatomy
Relevant bony anatomy: tibial tubercle, femoral trochlea, and patella
Patella: Composed of smaller medial facet, larger lateral facet, and odd (distal) facet; only medial and lateral facets covered in articular cartilage
Trochlear groove: Located at the anterior aspect of the distal femur; functions as bony constraint underlying patellofemoral stability
A shallow trochlear groove seen in the setting of trochlear dysplasia and associated with patellar instability
Medial patellofemoral ligament (MPFL): Provides static stability to the patella
Originates posterior and proximal to the medial epicondyle at Schottle point (Figure 1)
Functions as the primary constraint to lateral patellar translation from 0° to 20° of knee flexion
Medial and lateral retinacula: Provide static stability to the patellofemoral joint
Dynamic stability to the patellofemoral joint conferred primarily by the VMO, which is a medial restraint to lateral translation
Other relevant structures: Patellar tendon and distal quadriceps tendon
Blood supply: From the geniculate arteries
Pertinent History/Physical Examination Findings
History: Thorough history including any injury or trauma related to the onset of anterior knee pain
History of instability (dislocation or subluxation)
Radicular or hip symptoms: Rule out the lumbar spine or hip as an etiology
Effusion or swelling: May suggest intra-articular pathology such as a chondral injury
Crepitus and mechanical symptoms: May suggest chondral pathology or arthritis
Exacerbating activities such as squatting, ascending, descending stairs
Any previous treatments and surgeries
If previous physical therapy: Exercises and modalities, frequency and duration of therapy, and patient’s compliance
Physical examination
Standing alignment and gait
Valgus alignment: Higher risk of patellar instability and lateral facet overload
A double leg and single leg squat: may demonstrate dynamic valgus collapse, suggesting VMO and/or gluteal insufficiency
Figure 1 Lateral radiograph used to assess medial patellofemoral ligament femoral tunnel accuracy relative to Schottle point in a patient with a malpositioned femoral tunnel. Line 1 represents the posterior border of the cortex of the femur. Line 2 represents the superior border of the medial femoral condyle perpendicular to line 1. Line 3 represents the superior border of the notch parallel to line 2. Schottle point (A) is centered 1.3 mm anterior to line 1 and midway between lines 2 and 3. The center of the femoral tunnel (T). Distance from A to T in millimeters can be used to determine tunnel accuracy relative to Schottle point. (Reproduced with permission from Parikh SN: Patellar Instability: Management Principles and Operative Techniques, ed 1. Wolters Kluwer, 2019, Figure 38.1.)
The patient should be asked to identify the location of maximal pain, which is particularly helpful in patients with anterior knee pain
Focal pain at the proximal pole near the quadriceps tendon insertion or distal pole at the patellar tendon origin may suggest overuse or tendinopathy.
Seated examination
Active knee extension and flexion with the examiner’s hand over the patella
Patellar tracking and crepitus
J sign or lateral maltracking of the patella as the knee moves into extension out of the bony restraints of the trochlea
Resisted quadriceps strength testing: Compare with contralateral side
Supine examination
Hip range of motion: Identify any pain with range of motion
Femoral anteversion
Craig test (prone or supine): Palpate patient’s greater trochanter and passively internally rotate hip until its most prominent aspect is at its most lateral position
Passive straight leg raise to assess for radicular symptoms
Ask patient to contract the bilateral quadriceps; then compare the muscle bulk
Active straight leg raise to identify presence of a lag in extensor mechanism
Palpate the proximal, distal, medial, and lateral aspects of the patella
Place posteriorly directed pressure on the patella and ask the patient to contract the quadriceps, assessing for pain (patellar compression test)
Assess patellar tilt and the correctability of tilt
With the knee in full extension, place index finger and thumb around patella and determine if there is lateral tilt. If so, assess whether this can be corrected to neutral tilt within the trochlear groove.
Apply lateral-directed force to the medial border of the patella to assess the amount of lateral patellar translation and for patellar apprehension
Normal motion: less than two quadrants of patellar translation
If patellar instability is present, palpate medial border of the patella and medial epicondyle, assessing for tenderness and injury to the MPFL.
Palpate iliotibial band insertion on Gerdy tubercle and its course along the lateral femur; iliotibial band syndrome can cause anterolateral knee pain.
Determine Beighton score to assess for generalized ligamentous laxity.
Palpate medial and lateral infrapatellar tendon spaces: focal pain can indicate symptomatic fat pad impingement.
Synovial bands, or plica, may be located anteromedial, anterolateral, superomedial, or superolateral, and can cause symptomatic mechanical symptoms during knee motion; these areas can sometimes be palpated or may lie deep to muscle.
Relevant Imaging
Radiographs
Standardized knee radiographs: weight-bearing AP, PA Rosenberg (45°), lateral, and Merchant (or sunrise) axial radiographs
Axial view to assess depth of the trochlea, lateral subluxation, and tilt
Lateral view to evaluate trochlear morphology using criteria established by Dejour1
Also to assess for patella alta or patella baja; most often calculated using the Caton-Deschamps ratio (Figure 2)
Axial and lateral views to assess for patellofemoral joint space narrowing
Advanced imaging: Consider whether thorough history, physical examination, standardized radiographs fail to confirm a diagnosis.
MRI sensitive to the presence of pathology that may be incidental and either noncontributory or minimally contributory to the patient’s symptoms
May be obtained in the setting of patellar dislocations to assess for intra-articular loose chondral or osteochondral fragments, to assess the chondral surfaces of the patella and trochlea, and to assess other intra-articular structures, including the condyles and menisci
Figure 2 Patellar height measured on lateral radiograph. A, The preoperative Caton-Deschamps index measured 46.6/33 = 1.41. B, After isolated medial patellofemoral ligament (MPFL) reconstruction, the patellar height decreased to 40/33 = 1.21. The MPFL femoral tunnel is marked (black arrow). (Courtesy of Shital N. Parikh, MD, FACS.)
Presence of an effusion often suggests an intra-articular injury; MRI should be considered in this setting because plain radiographs cannot reliably establish a diagnosis
Effusion with associated anterior knee pain may occur secondary to chondral injury, osteochondral injury, a loose body, or arthritis; MRI can confirm diagnosis and guide treatment.
MRI can be used to calculate patellar indices, including the Caton-Deschamps ratio.
Also can be used to calculate the tibial tubercle-trochlear groove (TT-TG) distance, a measure of tibial tubercle lateralization that is associated with recurrent patellar instability2
TT-TG distance has been shown to be underestimated when measured on MRI compared with CT
CT may be considered to assess femoral anteversion (hip to knee CT), because excessive femoral anteversion can contribute to patellar instability.
Can be used in a similar manner as MRI to determine the TT-TG distance (Figure 3)
 Figure 3 Measurement of tibial tubercle-trochlear groove (TT-TG) distance on MRI. A, Superimposed axial images of the tibia and femur showing TT-TG distance. B and C, Alternative method of determining TT-TG distance by measuring from the edge of the image (or other common landmark) and subtracting. Simple geometry may be used to correct for rotation of the limb but usually is unnecessary. (Reproduced with permission from Chew FS: Musculoskeletal Imaging: The Essentials. Wolters Kluwer, 2018, Figure 21.19.) |
Nonsurgical Measures
Initial treatment for most causes of anterior knee pain and should be tailored to the specific diagnosis
NSAIDs may help with pain relief, but the most common causes of PFP are not inflammatory.
Physical therapy with a focus on VMO, hip, and core strengthening as well as improving squat mechanics
A home program should be performed daily.
A patellar cutout brace helpful in the setting of patellar maltracking
Compression sleeves without a patellar cutout may exacerbate symptoms; generally avoid in this setting.
Patellar taping: to improve patellar tilt or subluxation
Surgical Intervention
Indications depend on specific cause
Patients with loose chondral or osteochondral fragments, which may occur in the setting of a patellar dislocation: knee arthroscopy generally indicated, as the loose fragment(s) may damage healthy surrounding articular cartilage surfaces.
If osteochondral fragment is sufficiently large with enough attached bone to potentially heal, fixation may be attempted with a headless compression screw.
Skeletally immature patients: Fixation of chondral-only fragments3 or removal of fragments
Cartilage restoration procedure depends on age and activity level of patient and location of the lesion(s).
In the absence of a loose body, surgical intervention for PFP should occur only after a prolonged course of appropriate physical therapy with patient compliance.
MPFL Reconstruction
Indications
Commonly performed in the setting of recurrent patellar instability with an incompetent (stretched or torn) MPFL
First-time patellar dislocation: If no loose bodies, patients can be treated nonsurgically, with a progressive return to activities over 6 to 12 weeks.
Increasing data suggest MPFL reconstruction can be considered in patients with first-time patellar dislocation with multiple risk factors for recurrence—skeletally immaturity, trochlear dysplasia, patella alta.4
Recurrent patellar instability: Associated with patellar apprehension, tenderness to palpation along the course of the MPFL
(including on either the medial epicondyle or medial patellar facet), and increased lateral patellar translation
Effusion, particularly in the setting of a chondral or osteochondral injury
J sign on active knee extension
When actively extending the knee from a flexed position, the patella will move laterally as it exits the trochlear groove
Increased lateral patellar tilt: Examiner should determine whether correctible to neutral.
If lateral retinaculum is tight and tilt cannot be corrected, arthroscopic lateral retinacular release may be performed; rarely indicated in isolation
Axial radiographs may demonstrate a bony MPFL avulsion off the medial facet of the patella or the medial epicondyle; rarely represent intra-articular loose bodies
MRI may demonstrate midsubstance tear of the MPFL (most common) or a tear off its femoral or patellar insertion.
Chronic patellar instability: Tear may not be identified, but previously injured scar tissue may appear wavy or redundant.
Chondral surfaces should be evaluated preoperatively.
Most common locations of chondral injuries: Medial patella facet and lateral aspect of trochlea
Authors’ preferred technique
With patient under anesthesia, amount of patellar translation and end point assessed and compared with contralateral side
If patella not fully correctible to neutral, a lateral release may be considered
Incision: Along the medial border of the patella from the proximal pole to approximately the midpoint of the patella
Dissection is carried down through layer 1 (sartorial fascia) and layer 2, which contains the native MPFL, exposing the joint capsule.
Blunt dissection is performed between layers 2 and 3 from the medial border of the patella toward the medial epicondyle for later graft passage
The capsule can be carefully incised to demonstrate the patellar articular cartilage.
Two suture anchors are inserted as close to the cartilage as possible without violating, with the first near the proximal pole of the patella and the second just proximal to the midpoint.
Care must be taken to avoid penetrating the articular cartilage but also not to direct too far anteriorly so as to violate the anterior cortex of the patella.
Because there have been no differences shown in outcomes following allograft or autograft tissue, either a semitendinosus allograft or autograft can be used.
The center of the graft is marked and placed midway between the two suture anchors.
The sutures from each of the anchors are then tied over the graft, thereby securing the graft to the patella.
A small incision is made over the medial epicondyle.
Dissection is carried down to the medial epicondyle, taking care to protect the saphenous neurovascular bundle.
The saddle between the adductor tubercle and medial epicondyle is palpated and radiographically represented as Schottle point.
A guide pin is placed at this location under fluoroscopic guidance, directed proximally and anteriorly.
The graft can be shuttled through to the medial incision using the previously established interval.
Isometry can be tested using the guide pin and passing sutures placed into the graft.
Once isometry is confirmed, the guide pin can be overdrilled in preparation for an interference screw.
The guide pin is then pulled through along with the passing sutures placed into the graft.
The knee is placed at approximately 30° of flexion.
The patella should be held reduced in the trochlea and sufficient tension held on the sutures to keep it centered within the trochlea but not overtensioned.
The interference screw is then inserted.
Postoperative care
Weight bearing as tolerated with a hinged knee brace locked in full extension
Brace unlocked at postoperative week 6
Physical therapy begins within the first 2 to 4 weeks.
Return to sport: No sooner than 5 to 6 months after surgery
Tibial Tubercle Osteotomy
Indications
Performed for chondral surface overload or in setting of recurrent patellar instability with an increased TT-TG distance
In setting of recurrent patellar instability, MPFL reconstruction frequently performed concomitantly with tibial tubercle osteotomy
Approaches and techniques
The most common tibial tubercle osteotomy: Anteromedialization originally described by Fulkerson5 replaces:
Elmslie-Trillat, or purely medializing, tibial tubercle osteotomy: Historically used to medialize the tibial tubercle in the setting of tubercle lateralization and recurrent patellar instability
Maquet, or purely anteriorizing osteotomy: Historically used to anteriorize the tibial tubercle in the setting of patellar overload to decrease forces across the patellofemoral joint and offload areas of chondrosis
Shallow anteromedialization: Osteotomy made at an angle closer to the coronal plane than the sagittal plane; performed to medialize the tibial tubercle to a greater extent than it is anteriorized
Most commonly used in the setting of recurrent patellar instability with an increased TT-TG distance
Steep anteromedialization: Osteotomy made at an angle closer to the sagittal plane than the coronal plane; performed to anteriorize the tibial tubercle to a greater extent than it is medialized
Most commonly used in the setting of patellar chondrosis affecting the distal and lateral aspect of the patella
Equipment: Commercially available cutting guide or free-hand using Kirschner wires, osteotomes
Keep the proximal extent of the osteotomy at least 1 cm distal to the knee joint to prevent violating the articular cartilage.
Protect the patellar tendon at all times.
Unless distalization of the tubercle is planned, as in the setting of patella alta, the distalmost aspect of the osteotomized
tibial tubercle shingle may be left intact to minimize the risk of nonunion.
Drill holes for the screws should be made in the anterior aspect of the tubercle before performing the osteotomy cut.
Once osteotomy is performed, the tubercle can be moved anteromedially by the templated distance.
A Kirschner wire may be placed away from the planned location of screws to maintain the planned reduction
4.5-mm cortical screws may then be placed in lag fashion (Figure 4).
A washer may be used on the proximal screw because of poor metaphyseal bone quality in that location.
Postoperative care
Toe-touch weight bearing for the first 6 weeks postoperatively
Immediate passive range of motion from 0° to 90°
Straight leg raises and quadriceps sets to prevent quadriceps inhibition
Active and active-assisted knee extension not permitted until 6 weeks after surgery
Return to sport: No earlier than approximately 6 months postoperatively following a criteria-based return to sport battery of testing
Cartilage Restoration
Indications
Considered in the setting of high-grade (grade 3 or 4) symptomatic chondral lesions
Common presenting signs and symptoms: Recurrent effusions, mechanical symptoms such as catching, pain when the patellofemoral joint is loaded, such as with deep squatting or stair climbing
Débridement alone, or chondroplasty, may be considered in older patients (at least age 50 years) without patellofemoral osteoarthritis, in whom the results of cartilage restoration surgery are less predictable and as a staged procedure if autologous cell-based surgery, such as
matrix-induced autologous chondrocyte implantation (MACI) is planned.
Figure 4 A and B, Demonstration of a final pictorial representation of the tibial tubercle osteotomy procedure. The broad cancellous base allows for optimal healing. C and D, A schema demonstrating a medialization cut and an oblique cut (anteromedialization), highlighting the amount of correction that can be gained. (Reproduced with permission from Cordasco F, Green D: Pediatric and Adolescent Knee Surgery. Wolters Kluwer, 2015, Figure 19.8.)
MACI requires a biopsy and for the harvested cells to be expanded ex vivo before implantation.
Chondroplasty alone may provide sufficient relief of symptoms in these patients, and the second-stage procedure is not necessary.
Single-stage cell-based treatments also exist, most commonly in the form of particulated juvenile chondrocytes.
These are commercially available but often require a special order and must be used within a certain time period before expiration.
Cell-based cartilage restoration techniques can be used only when there are no cystic changes or intralesional osteophytes within the subchondral bone.
Subchondral marrow edema alone without the aforementioned degenerative changes is not a contraindication for cell-based strategies.
Osteochondral autograft transplantation (OAT) and osteochondral allograft (OCA) are options for symptomatic chondral or osteochondral lesions of the patellofemoral joint.7
OAT: For lesions less than 1.5 to 2 cm2, depending on the size of the patient’s knee
OCA: For larger lesions but may take longer to incorporate than autograft tissue
Approaches and techniques
Typically performed via a small medial parapatellar arthrotomy; allows eversion of the patella and access to the entire patella and trochlea
Violate as little of the extensor mechanism as necessary to evert the patella and access the pathology.
Excise the retropatellar fat pad to help facilitate patellar eversion.
Cell-based technique (MACI or juvenile particulated chondrocytes)6
Débride lesion to a stable rim of healthy cartilage.
Use no. 15 blade and curets (ringed or conventional), taking care to remove the calcified cartilage layer but avoid violating the subchondral bone.
The lesion can then be sized before implanting the cell suspension.
A thin layer of fibrin glue is typically placed at the base of the lesion before inserting the cells, and then above the cells to seal them in.
No irrigation is used after the cells are placed within the lesion.
Osteochondral autograft transplantation
Autograft plugs up to 1 cm2 harvested from the intercondylar notch or from the periphery of the trochlea, most commonly the superolateral aspect of the trochlea
The recipient site is prepared in a similar fashion as the donor plugs are harvested.
The injured cartilage and subchondral bone are removed with a core harvester, typically to a depth of 1 cm.
When performing OAT on the patella, a guide pin and reamer are recommended rather than a manual harvester, because the subchondral bone is often harder than femoral and trochlear subchondral bone.
The depth of the recipient site is confirmed, and the donor plugs are carefully impacted, typically using a delivery tube, to fill the lesion.
It is important that the plugs are flush with the surrounding healthy articular cartilage and not proud, as this will predispose to shearing of the donor plugs and graft failure.
Osteochondral allograft
Although allograft plugs are most commonly taken from a donor femoral condyle, a bulk trochlea or patella may also be used but can be difficult to procure.
Authors’ preference: Use circular allograft plugs, which can be sized up to 18 mm2 each and overlap each other
Measure chondral lesion, or recipient site, to determine how many and what size plugs are needed to reconstruct the defect.
A guide pin is then placed through a sizer, and the recipient site prepared for implantation of a donor plug.
Reaming is typically performed no deeper than 8 mm
The dimensions of the recipient site are measured, and a donor plug of those same dimensions is harvested from the OCA.
The plug is then impacted to fill the recipient site, and the process repeated if additional plugs are needed (Figure 5).
Although a press fit is typically used, chondral darts or headless compression screws may be considered as supplemental fixation.
Figure 5 Photograph shows osteochondral allograft transplantation for cartilage lesions in the trochlea. (Reproduced with permission from Rubash HE: The Adult Knee, ed 2. Wolters Kluwer, 2020, Figure 20.3.)
Postoperative care
Rehabilitation protocols vary.
Typically, the knee remains locked in full extension when ambulating with the assistance of crutches for at least the first 6 weeks postoperatively.
If early weight bearing allowed, should be with a brace locked in full extension to prevent graft shearing
Early motion and quadriceps contractions, including straight leg raises and quad sets, encouraged immediately
Return to sport: Typically no sooner than 5 to 6 months after surgery when the athlete passes a criteria-based return to sport battery of testing
Top 10 Knowledge Drops for Your Rotation
The most common cause of PFP is patellar maltracking resulting from a muscular imbalance, which includes a weak VMO and hip abductors.
A hip examination and gait assessment should be performed for all patients with knee pain, because femoral anteversion and internal tibial torsion can contribute to patellar instability as well as chondral overload.
The TT-TG distance may be measured using CT or MRI. The distance is underestimated by approximately 10% on MRI as compared with CT.
The Caton-Deschamps ratio may be used to assess for patella alta. Values greater than 1.3 are considered abnormal.
Factors predisposing to recurrent patellar instability include skeletal immaturity, trochlear dysplasia, patella alta, and lateralization of the tibial tubercle.
Lateral retinacular release should rarely, if ever, be performed in isolation and may be considered in conjunction with other procedures if the patella cannot be manually corrected to neutral.
An anteriorizing tibial tubercle osteotomy is typically used to decrease patellofemoral contact forces, whereas a medializing tibial tubercle osteotomy is used to treat recurrent patellar instability with increased TT-TG distance.
During MPFL reconstruction, the femoral insertion of the MPFL graft is at an isometric point located between the medial epicondyle and adductor tubercle. Radiographically, this is represented by Schottle point, which is just proximal to Blumensaat line and anterior to the posterior femoral cortical extension line.
Cell-based cartilage restoration treatments (eg, MACI, juvenile particulated chondrocyte implantation) should not be performed if there are degenerative changes of the subchondral bone.
When performing OAT or OCA, the implanted plugs must not sit proud relative to the surrounding articular cartilage, as this may result in shearing and graft failure.
MENISCUS TEARS
Meniscus tears are among the most common pathologies encountered by orthopaedic surgeons. Meniscus tears can be acute/traumatic, most often occurring from a twisting or pivoting injury, or degenerative, although the distinction is not always clear. They can occur in isolation or combined with a knee ligament injury, most frequently an anterior cruciate ligament (ACL) tear. Acute meniscus tears in young athletes, with or without a concomitant ACL injury, more commonly affect the lateral meniscus, whereas degenerative tears most commonly affect the posterior horn of the medial meniscus, although there is considerable overlap. The menisci play a number of important roles in the knee, including decreasing the contact forces between the tibia and femur. Therefore, the menisci should be preserved whenever possible. Because the meniscus has a limited blood supply, primarily in the periphery, not all tears are considered repairable.
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