21-year-old man with recurrent patellar instability
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A 21-year-old man presented with bilateral knee recurrent patellar instability.
His first dislocation occurred on the right side after a misstep 8 years prior, and he has since dislocated innumerable times with everyday activities, such as walking and stair climbing.
On examination of the right lower extremity, he had a patellar J sign and grade 3 lateral translation with significant apprehension. His right hip demonstrated external rotation of 45° and internal rotation to 60°.
Radiographs demonstrated preserved joint spaces and no osteochondral lesions. Bilateral patella alta are appreciated. The right Caton-Deschamps index (CDI) was 1.34. A crossover sign was noted with lateral trochlear convexity and medial trochlear hypoplasia, consistent with Dejour-type C dysplasia (Figure 1). Full-length lower extremity films demonstrated valgus alignment (Figure 2). MRI of the right knee demonstrated lateral patellar subluxation and attenuation of the medial retinaculum at the patellar insertion (Figure 3). The tibial tubercle to trochlear groove (TT-TG) distance was 21 mm. CT femoral version studies demonstrated femoral anteversion of 32.8° on the right (Figure 4).
Source: Abigail Campbell, MD; Alexander Golant, MD; Kevin Lehane, DO; Allison Morgan, MD
What are the best next steps in management of this patient?
See answer below.
Distal femur and tibial tubercle osteotomy and MQTFL reconstruction
The patient was positioned supine with a nonsterile thigh tourniquet and a radiolucent foam ramp. Examination under anesthesia confirmed lateral translation of three or more quadrants without a firm endpoint.
There was no “jumping J” sign, supporting the decision to proceed without trochleoplasty. A diagnostic arthroscopy was performed first to ensure the absence of cartilage lesions and visualize the lateral positioning of the patella (Figure 5).
MQTFL reconstruction
For the open procedures, a single longitudinal incision from the distal femur to 5 cm distal to the tibial tubercle was made.
Through this incision, a semitendinosus allograft 5.5 mm in diameter for medial quadriceps tendon femoral ligament (MQTFL) reconstruction was fixed on the femur using Schottle’s point for identification under fluoroscopy and was confirmed with direct palpation of the saddle between the medial femoral epicondyle and the adductor tubercle (Figure 6). It was secured with a 6-mm x 20-mm interference screw and protected in a laparotomy sponge until the osteotomies were complete.
Distal femur osteotomy
After accessing the distal femur via an extended medial parapatellar arthrotomy, a patient-specific guide (Bodycad) was used to make the osteotomy (Figure 7a). This was 3D-printed to execute a correction of 13° of external rotation and 7.8° of varus. The guide was secured to bone with two unicortical screws and two K-wires, which both confirmed appropriate position according to the preoperative plan (Figure 7b). The off-axis K-wires would later be used to assess subsequent derotation.
As the planned osteotomy was derotational, this necessitated violation of the lateral hinge. Thus, prior to completion of the cut, a provisional external fixator was placed with two anterior pins: one in the shaft proximally and one in the metaphysis distal to the osteotomy site, connected by a single bar (Figure 7c). Once the osteotomy was complete, the medial gap was closed with manual pressure and then the external fixator was loosened to allow gentle external rotation of the distal femur until the K-wires (Figure 7d) were coplanar and the precontoured patient-specific plate was able to slide over it (Figure 7e).
The plate was first reduced to bone with a 4.5-mm non-locking screw and then secured with six additional 4.5-mm locking screws. Successful execution of the plan was confirmed by flush plate positioning and intraoperative fluoroscopy utilizing an alignment rod from the center of the femoral head to the center of the talus, which passed through the center of the knee joint, between the tibial spines (Figure 7f).
Tibial tubercle osteotomy
For the tibial tubercle osteotomy (TTO), the patellar tendon was mobilized and the tubercle was exposed by subperiosteally elevating the anterior compartment musculature in one sleeve. The patient-specific guide was planned for anteriorization of 7 mm, medialization of 8 mm and distalization of 6 mm. Two additional cuts were made: one across the proximal tubercle and a counter-cut on the lateral side. Violation of the distal periosteal hinge was required to enable distalization of the fragment. Fluoroscopy confirmed normalization of the CDI (Figure 8).
The tubercle was then secured with two parallel K-wires and an additional out-of-plane derotational wire. The two parallel wires were then overdrilled, countersunk and two 5-mm cannulated headless compression screws were placed. Autologous cancellous bone from the removed distal femur wedge and 5 mL of a commercially available bone-void filler (hydroxyapatite + calcium sulfate) were utilized to fill the osteotomy site.
Lateral release, MQTFL completion
The lateral retinaculum was incised through its superficial layer immediately adjacent to the patella from vastus lateralis proximally to the patellar tendon distally. The deep layer was incised along the same length, but 1 cm posteriorly. Given persistent lateral tightness, a decision was made intraoperatively to release rather than lengthen. Returning our attention medially, the MQTFL allograft, previously fixed on the femur, was passed through a plane in layer two of the knee and through a central slit in the quadriceps tendon. Once the arthrotomy was closed, the MQTFL was tensioned and sutured to itself using 1.3-mm nonabsorbable SutureTape (Arthrex) in 20° of flexion. Intraoperative range of motion (ROM) of the knee demonstrated graft isometry between 0° and 90°.
Final ROM and stability testing was performed, with flexion to more than 130°, full extension, central tracking of the patella and about one quadrant of lateral translation of the patella with a firm end point. A layered closure was performed.
Postoperative rehabilitation
During the first week postoperatively, the right lower extremity was maintained non-weight-bearing in a brace locked in extension. Weight-bearing was advanced to 30% at week 3, 50% at week 5 and weight-bearing as tolerated at week 8.
The brace was unlocked while seated or supine for ROM from 0° to 90° at week 2 and to 120° at week 5. It was kept locked in extension while weight-bearing until quadriceps strength was full.
Discussion
The ongoing debate in treatment and a myriad of surgical options available for patellar instability are representative of the complex underlying pathology that manifest in a dislocating patella. Patellar stability relies on soft tissue restraint, with dislocations occurring when there is injury or attenuation of the medial patellofemoral ligament/MQTFL. In addition, osseous constraints are also critical and variations in anatomy of the femur, patella and tibia may all predispose a patient to patellar instability secondary to maltracking.
In general, a lateralized tibial tubercle, evidenced by TT-TG distance more than 20 mm or TT-PCL more than 24 mm, may be addressed with a medializing and usually anteriorizing TTO. Trochlear dysplasia, as graded by the Dejour classification, may be treated with trochleoplasty or may be accounted for with other osseous corrections, such as the tibial tubercle anteromedialization.
Patella alta, defined by a CDI of more than 1.3, is addressed with a distalizing TTO. Patellar tilt of more than 20° may be treated with lateral retinacular lengthening or release. Valgus malalignment of more than 5° of the lower limb may be addressed with either lateral opening wedge or medial closing wedge osteotomy of the distal femur.
Finally, increased femoral anteversion more than 25° may be addressed with derotational distal femur osteotomy. Often, combined procedures are necessary to address various components underlying instability.
The distal femur derotational osteotomy is a relatively recent addition to the patellar stabilization armamentarium. Increased femoral anteversion increases Q-angle and may be first detected clinically by increased internal rotation of the hip. Increased femoral anteversion has been observed in patients with patellar instability compared with matched controls, and thus has been identified as an additional target to normalize the proximal force vector on the patella. However, published cutoffs for pathologic elevation vary from 20° to 30°. Good clinical outcomes with low dislocation rates have been described following derotational distal femur osteotomy.
Kuo Hao and colleagues retrospectively reviewed data for 67 patients with patellar instability and increased femoral anteversion (greater than 25°), of whom 36 underwent isolated MPFL reconstruction and 31 underwent MPFL reconstruction with derotational distal femur osteotomy. While both groups had good outcomes and no redislocations, the distal femur osteotomy cohort had significantly better patient-reported outcome measures (Lysholm, IKDC and Kujala scores).
In their 2024 systematic review of 11 studies with 569 knees, Daofeng Wang, MD, and colleagues reported derotational distal femur osteotomies decreased femoral anteversion from 33.6° to 13° with significant improvements in Lysholm score (weighted mean: 55.5 vs. 80.4), IKDC score (weighted mean: 52.8 vs. 78.6) and Kujala score (weighted mean: 54.5 vs. 80.6).
Antonio Klasan, MD, PhD, and colleagues performed a similar systemic review and highlighted six studies that reported a decrease in TT-TG, given the femoral osteotomy changes the position of the trochlear groove. This is critical to recognize when planning concomitant distal femur osteotomy and TTO and necessitates the distal femur osteotomy be performed first.
Key points
- It is critical to analyze and identify all contributing anatomic factors in the patient with recurrent patellar instability.
- For patients with excessive femoral anteversion (greater than 25°), derotational distal femur osteotomy increases patellar stability with improved patient outcomes and low rates of recurrent dislocation.
- In cases where multiple surgical procedures are necessary, meticulous surgical planning and order of operations is crucial. A derotational distal femur osteotomy should be completed prior to TTO, and all osseous corrections should be completed prior to soft tissue tensioning.
- With combined coronal plane and rotational distal femur osteotomies, patient-specific instrumentation may enhance accurate execution.
- References:
- Chen X, et al. Orthop J Sports Med. 2023;doi:10.177/23259671231181937.
- Dejour DH, et al. J Exp Orthop. 2021;doi:10.1186/s40634-021-00348-7.
- Diederichs G, et al. Am J Sports Med. 2013;doi:10.1177/0363546512466396.
- Duerr RA, et al. JBJS Rev. 2016;doi:10.2106/JBJS.RVW.O.00046.
- Frosch KH, et al. Arch Orthop Trauma Surg. 2016;doi:10.1007/s00402-016-2431-4.
- Hao K, et al. Knee Surg Sports Traumatol Arthrosc. 2023;doi:10.1007/s00167-022-07308-3.
- Hinz M, et al. Knee Surg Sports Traumatol Arthrosc. 2023;doi:10.1007/s00167-023-06904-5.
- Klasan A, et al. J Exp Orthop. 2024;doi:10.1186/s40634-024-00346-y.
- Steensen RN, et al. Am J Sports Med. 2015;doi:10.1177/0363546514563903.
- Swarup I, et al. Knee. 2017;doi:10.1016/j.knee.2017.02.012.
- Wang D, et al. Knee Surg Sports Traumatol Arthrosc. 2024;doi:10.1007/s00167-023-06724-7.
- Zhang Z, et al. Orthop J Sports Med. 2021;doi:10.1177/23259671211057126.
- For more information:
- Abigail Campbell, MD; Alexander Golant, MD; Kevin Lehane, DO; and Allison Morgan, MD, can be reached at NYU Langone Orthopedic Hospital in New York. Morgan’s email: Allison.morgan@nyulangone.org.
- Edited by Nicole Rynecki, MD, and Harold I. Salmons, MD. Rynecki is a chief resident in orthopedic surgery at NYU Langone. She will be pursuing a sports medicine fellowship at Hospital for Special Surgery following residency completion. Salmons is a chief orthopedic surgery resident at the Mayo Clinic. He will be pursuing an adult reconstruction fellowship at Hospital for Special Surgery following residency completion. For more information on submitting Orthopedics Today Grand Rounds cases, please email orthopedics@healio.com.
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