Knee Flashcards
Define Patellofemoral instability
Encompasses a broad spectrum of instability from frank dislocation to subluxation
Factors predisposing to PFJ instability
BONY
- Patella Alta
- Trochlea dysplasia
- Lateral Femoral condyle dysplasia
- Patealla dysplasia
SOFT TISSUE
- Ligamentous Laxity
- MPFL Injury
- VMO atrophy / high insertion
- VL hypertrophy
- Tight Lateral Structures (ITB, VL, Capsule)
ALIGNMENT
- Femoral Anteversion
- External Tibial Torsion
- Lateral Tibial Tuberosity
- Genu Valgum
- Pes Planus
- Increased Q Angle
Define Q Angle
Angle Subtended by a line drawn from the ASIS to centre of patella and the centre of the patella to the tibial tuberosity
Male = 10, Female = 15
Pathological Male >15, Female >20
Schottle’s Point
Anatomic isometric insertion of the MPFL Defined at the point 1mm anterosuperior to the intersection of two lines
- a line extending from the posterior cortex and another
- perpendicular to the first, just proximal to the most posterior point of Blumensaat’s Line
MPFL
Medial Patellofemoral Ligament
- Primary Stabiliser of the Patella
- Extrasynovial ligament that runs transversely from the MFC to the patella in Layer II
- Most often injured on the femoral side
- Femoral Insertion - MFC midway between adductor tubercle and medial epicondyle
- Patella Insertion - Proximal 1/2 medial border of patella
Algorithm of Tx for PFJ Instability
o Patella Alta: - TTT Distalisation
o ↑ TTTG: - TTT Medialisation
o MPFL Tear: - MPFL Reconstruction
o Patellar Tilt: - Lateral Release
o Severe Trochlear Dysplasia: - Trochleoplasty (uncommonly performed)
o ↑ Femoral Anteversion: - Femoral Derotation Osteotomy
o External Tibial Torsion: - Tibial Derotation Osteotomy
Patella Height Measurements
Insall- Salvati Method
- Insall-Salvati method measures the greatest diagonal longitudinal length of the patella (usually from superoposterior corner to inferior pole) and the length of the inferior pole of patella to the tibial tuberosity (the posterior border of the patella tendon)
- This ratio is A/B, with patella tendon (A) and patella height (B).
- Normal ratio is 1.0 + 0.2.
- Patella alta has a high ratio >1.2.
- Patella infera (baja) has a low ratio <0.8.
Blackburne-Peele Method
- Blackburne-Peele method measures the longitudinal length of the patella articular surface and the length of the inferior patellar articular surface to the perpendicular joint line.
- This ratio is A/B, with inferior articular surface to joint line (A) and patella articular surface (B).
- Normal ratio is 0.8 + 0.2.
- Patella alta has a high ratio >1.0.
- Patella infera (baja) has a low ratio <0.8.
Caton Deschamps Method
- Caton-Deschamps Index is similar to ISI and BPI.
- It is a ratio of the posterior articular length of the patella and the length from the inferior pole to the superoanterior tip of the tibia.
- Normal is 1.0 +/-0.2.
- Patella alta is > 1.2
- Patella infera is <0.8.
Trochlear Morphology
Trochlear Depth = < 8mm = shallow
Bump Sign
- If line of floor where it joins the ant cortex has a bump Patella will not engage properly
- Bump >3mm is abnormal
The Crossing Sign
- A primary radiographic indication of trochlear dysplasia and is visualized when the line representing the trochlear floor crosses the anterior border of the femoral condyles
- Can be combined with a TROCHLEAR SPUR
Radiologic Trochlear Angles
Sulcus Angle
- Sulcus Angle is the depth of convexity of the trochlear groove.
- Angle made with lines from centre of trochlear groove to highest point of medial and lateral femoral condyles.
- Normal angle is 136° + 6.
- > 145 = dysplasia
Subluxation (Patellofemoral congruence angle of Merchant)
- Angular difference between
- line bisecting the sulcus angle &
- line from sulcus apex to the lowest point on patella
- Medial direction is –ve
- Merchant (JBJS Am 1974)
- 100 Normal subjects - Normal = –6 ± SD11°
- 25 recurrent dislocators - +23°
- AbN = greater than 16o
Lateral tilt - Laurin’s lines
- Line along lateral patellar facet
- Line b/w most prominent ant points of trochlea
- Normal = Lines should diverge laterally
- Laurin 1978
- 100 Normal - 97% opened laterally
- 30 Recurrent subluxators - 80% parallel & 20% opened medially
Patella Radiologic Investigations
- All patients post an acute dislocation should have XRAYS & MRI (look for concomitant osteochondral lesions which occur in 30%)
- Radiological investigations include
- XRAYS (AP WEIGHT BEARING / LATERAL [30° FLEXION] / SKYLINE [MERCHANT 45°])
- Coronal Plane Deformity – 3 FOOT STANDING FILMS
- Patella Height (Insall-Salvati / Blackburne Peele / Blumensaats/Caton-Deschamps)
- Trochlear Morphology
- Crossing Sign (Lateral)
- Sulcus Angle (Skyline)
- Patella Tilt
- CT (TTTG)
- Lower Limb Version – PERTH PROTOCOL/SCANNOGRAM
- TTTG
- Patella Tilt
- Sulcus Angle
- MRI
- Bone Bruising
- Chondral Injury
- MPFL Injury
- XRAYS (AP WEIGHT BEARING / LATERAL [30° FLEXION] / SKYLINE [MERCHANT 45°])
Tibial Tubercle Trochlear Groove Angle
- TTTG angle represents relationship of centre of deepest part of trochlear sulcus & tibial tuberosity.
- Assessment of TTTG by superimposing the trochlear groove and tibial tuberosity on axial CT.
- Horizontal line is drawn from the posterior femoral condyles.
- Perpendicular line is drawn to the deepest part of the trochlear groove and the anterior part of the tibial tubercle.
- The distance between the 2 lines is the TTTG.
- Normal TTTG is 10-12mm.
- TTTG > 20mm is an indication for TTT.
- TTTG b/w 12-20mm is the grey area for TTT treatment.
Medial Knee Layers
Layer 1
- Fascia
- Sartorius
Layer 2
- Superficial MCL
- POL (Posterior Oblique Ligament)
- MPFL
- Semimembranosus
Layer 3
- Deep MCL
- Capsule
- Coronary Ligament
Lateral Knee Layers
Layer 1
- ITB
- Biceps
Layer 2
- PF retinaculum
- LPFL
Layer 3 Superficial
- LCL
- Fabellofibular Ligament
Layer 3 Deep
- Popliteus tendon
- Popliteofibular ligament
- Arcuate Ligament
- Coronary Ligament
- Capsule
Covertry Criteria for HTO
COVENTRY (Long Term Results of Upper Tibial Osteotomy for Degenerative Arthritis of the Knee – Acta Orthopaedic Belgium 1982) published results of his criteria for HTO. There are 7 criteria:
- Age <65 Years / Physically Active
- Pain Correlated with Radiological Changes (Medial)
- Radiologically Normal Lateral Compartment
- Varus Deformity < 15°
- FFD < 15° / ROM > 90°
- Stable Knee (Cruciate Intact)
- Internal Derangements Excluded
Indications for HTO
- 3/12 failed NON-OT Mx
- Age < 55 years
- Physically Active
- Unicompartmental OA (Clinically & Radiologically [MRI])
- Asymptomatic Mild PFJ OA
- FFD <15°
- Varus Deformity <10
- SUBLUXATION < 1CM
- ROM > 90°
- Stable Knee (Cruciate Intact)
- Weight < 90 kg
- Non-Inflammatory Arthritis