Recurrent patellar dislocation is a common clinical condition. Previous treatment methods include release of the lateral patellar support band, tight overlapping sutures of the medial patellar support band, internal tibial tuberosity osteotomy, and medial femoral stop transposition, etc. Recently, medial patellofemoral ligament (MPFL) reconstruction has achieved good clinical results for the treatment of recurrent patellar dislocation. The clinical characteristics of recurrent patellar dislocation and the anatomy, isometricity and reconstructive surgical methods of MPFL are reviewed.
1. What is the current status of research on the anatomy, mechanics, and isometric properties of MPFL?
1.1 Anatomy of MPFL?
The stable structures of the patellofemoral joint include the medial and lateral patellar support band complex, including the patellofemoral ligament and the patellofemoral tibial ligament. The patellofemoral meniscal ligament has also been mentioned in the recent literature.
In 1979, Warren and Marshall performed dissections on 154 freshly frozen cadaveric specimens to provide a detailed description of the medial structures of the knee joint. They divided the medial structures of the knee into three layers: the first layer consisted of the deep fascia or femoral fascia, the second layer consisted of the superficial layer of the medial collateral ligament and structures anterior to the medial collateral ligament, and the third layer consisted of the deep layer of the medial collateral ligament and the knee capsule. They considered the MPFL to be an extra-articular structure along with the superficial layer of the medial collateral ligament.
Recently, Panagiotopoulos and Strzelczyk et al. described in detail the anatomy and biomechanical function of the medial stabilizing structures of the knee joint in eight cadavers. The normal MPFL starts on the ridge between the medial femoral epicondyle and the adductor tuberosity and ends outward in the upper 1/2 of the medial patellar border, with its superficial fibers extending posteriorly to the posterior joint capsule and fusing with it. the length of the MPFL from the starting point to the end point averaged 47.37 mm, and the width at the femoral stop ranged from 10 to 20 mm (mean 14.87 mm) and from 20 to 30 mm at the patellar stop (mean 25.25 mm). Because the MPFL is small at the femoral stop, this anatomical feature dictates that single-point fixation can be used in reconstructive surgery.
Steensen and Dopirak found that the average distance from the superior pole of the patella to the superior edge of the MPFL (between the ABs) was 6.1 mm, which corresponds to the position at the superior medial corner of the patella. The mean distance from the superior pole of the patella to the inferior edge of the MPFL (between AC) was 23.1 mm, which corresponds approximately to the midpoint of the medial patellar border (Figure 1). the vertical height of the MPFL at the patellar stop corresponds to 38.8% of the patellar height. On the femoral side, the MPFL stops directly at the medial epicondyle of the femur, and the lower edge of the MPFL femoral stop is adjacent to the upper edge of the MCL femoral stop.
1.2 What is the mechanical role of the MPFL?
The MPFL is the primary stabilizing structure limiting lateral patellar dislocation. conlan et al.20] evaluated 25 cadaveric knees and analyzed the soft tissue stabilizing structures limiting lateral patellar dislocation and found that the MPFL provided 53% of the overall limiting force. a study by desio et al. showed similar results and concluded that the MPFL provided 60% of the limiting force .
Sandmeier et al. used a cadaveric knee to sever the medial stabilizing structures to simulate patellar dislocation and then used autografts to reconstruct the MPFL to assess the effect of the MPFL on the patellar trajectory. When the patella was externally pushed, the patellar trajectory was significantly altered after cutting the medial stabilizing structures of the patella, and reconstruction of the MPFL was able to restore and normalize the patellar trajectory.
It is generally believed that there are many predisposing factors for patellar dislocation, such as abnormalities in soft tissue and bone structure. The importance of the MPFL was emphasized in Noruma’s study, which found a very high incidence of MPFL injury in cases of acute patellar dislocation and an abnormal MPFL in all cases of old patellar dislocation.
Therefore, it was concluded that MPFL injury or defect is the main causative factor for recurrent patellar dislocation or patellar instability after acute patellar dislocation.
1.3 Isometric study of MPFL?
A study of MPFL isometricity by Steensen and Dopirak showed three sets of data showing better isometricity – lower edge of the MPFL patellar stop to the upper edge of the femoral stop, midpoint to the upper edge, and upper edge to the upper edge. During knee flexion from 0 to 90 degrees, these distances were: lower edge to upper edge = 1.1 mm, midpoint to upper edge = 1.8 mm, and upper edge to upper edge = 2.4 mm; while in the range of knee flexion from 0 to 120 degrees, their lengths were 2.3 mm, 3.5 mm, and 4.0 mm, respectively. the other point isometries were not as good as these three groups.
Statistics showed that the most important point affecting isometric length was the MPFL femoral stop. The patellar stop point, on the other hand, did not have a significant effect on isometric properties.
In MPFL reconstructive surgery, if the patient’s own MPFL has disappeared (e.g., if there is heavy soft tissue damage after acute patellar dislocation, or if the medial structures are scarred in patients with recurrent dislocation), these anatomical landmarks can be used for localization. The femoral stop is located slightly superior to the anterior aspect of the medial epicondyle of the femur. Also, the lower edge of the MPFL patellar stop is generally 23.1 mm from the superior pole of the patella, and this point is approximately at the midpoint of the medial edge of the patella.
2, Classification of MPFL injuries after patellar dislocation?
Nomura et al. analyzed 67 knees in 63 patients, and the general type of MPFL injury was explored intraoperatively. Acute patellar dislocation was defined as the time from the first patellar dislocation to surgery being less than 3 weeks, and old patellar dislocation was defined as patellar dislocation occurring at least twice or more, or symptoms of patellar instability persisting for more than 3 months after the first patellar dislocation.
2.1 Acute patellar dislocation?
MPFL injuries with acute patellar dislocation can be divided into 2 types: (1) deattachment and (2) parenchymal tear (rupture). An avulsion is defined as a deep MPFL tear from the point of attachment of the femur, but the ligament itself is not ruptured. A parenchymal tear is defined as a complete tear or rupture of the MPFL. Since the MPFL narrows and thins close to its femoral attachment point, parenchymal tears of the MPFL often occur near the femoral stop.
Sallay et al. performed an incision in 16 patients with patellar dislocation and found that 94% of patients had a tear of the MPFL near the femoral stop.
2.2 Obsolete patellar dislocation?
In all patients with old patellar dislocation, no normal MPFL structures were found intraoperatively. They can be classified into 3 types based on what was seen intraoperatively.
Type 1: femoral stop detachment (loose). The MPFL appears to be “intact” intraoperatively, but it is actually “loose” because the MPFL is detached from the femur at its attachment point and has no solid stop, and may only have a small amount of scar tissue attached.
Type 2: This type of MPFL is partially scar tissue, or is connected to the MCL and/or adductor nodes by abnormal scar tissue. This type of abnormal scar tissue formation is often located near the femoral attachment point of the MPFL, and all type 2 MPFL injuries can result in MPFL laxity due to “lengthening” of the MPFL itself or abnormalities of its attachment point.
Type 3: In this type of MPFL injury, the MPFL appears to have completely disappeared (absent type), and the MPFL is found to have completely disappeared intraoperatively, or only a small amount of ligament fibers remain, but the continuity of the ligament is lost.
3. The technique of MPFL reconstruction surgery?
The methods of MPFL reconstruction by Fithian using autologous semitendinosus tendon double bundle, Nomura using artificial ligament, Teitge using autologous internal retractor tendon transposition, Schottle and Carmont using autologous semitendinosus tendon or thin femoral tendon, and Camanho using medial 1/3 patellar tendon have been reviewed. These reconstruction methods have their own characteristics in terms of graft selection and fixation, but the selection of patellar and femoral stops for the MPFL is basically the same. A search of the literature revealed that the most commonly used graft in MPFL reconstruction surgery is the autologous N cord tendon, followed by allograft tendon and artificial ligament, but the differences in their surgical approaches are not significant. In this paper, we mainly present the method of MPFL reconstruction based on Fithian’s double bundle.
3.1 Arthroscopy?
Regardless of the surgical method used, the mobility of the patella is first assessed after the onset of anesthesia. Fithian et al. proposed a diagnosis of patellar instability based on a “soft” or absent endpoint when the patella is dislocated laterally in the fully extended or flexed 30ºposition of the knee; and a “soft” or absent endpoint when the patella is dislocated in the flexed 30ºposition of the knee. º position, the patella can be pushed more than 10 mm laterally (from the central position).
A standard arthroscopic approach was then established for diagnostic arthroscopy. The anterolateral and anteromedial approaches are used, and an external superior approach is used – the external superior approach allows easy examination of the patellar cartilage surface, and it is also easy to examine the patellar trajectory and patellar mobility. The accompanying articular cartilage injuries are examined in detail and documented, and if unstable cartilage fragments are present, they need to be removed and other injuries treated symptomatically.
3.2 Graft acquisition?
There are many graft options available for MPFL reconstruction, including autografts, allografts, and artificial ligaments. Autologous grafts can include autologous semitendinosus tendon, thin femoral tendon, adductor tendon, quadriceps tendon, patellar ligament, iliotibial bundle, broad fascia, etc.; allografts include allogeneic bone-patellar tendon complex, allogeneic anterior tibial tendon or semitendinosus tendon, etc.; some people also choose artificial ligaments.
The graft is cut according to the type of graft to be used intraoperatively. The length of the MPFL is usually about 50 mm, and the length of the required tendon is about 15-20 cm depending on the fixation method. In most cases, the autologous semitendinosus tendon or thin femoral tendon can meet the need. The free end of the graft is closed with a locking suture using a No. 2 Ethibond nonabsorbable suture, and the trailing end of the suture is used as a traction line. The graft is then placed on the graft preparation table and pre-tensioned for traction. Single-strand or double-strand reconstruction can be chosen so that the tendon is treated slightly differently.
3.3 MPFL patellar stop selection, preparation of the patellar tunnel?
A longitudinal incision is made at the medial edge of the patella, approximately 3 cm in length, and the subcutaneous tissue is bluntly separated with a finger through the incision and the superior pole of the patella and the medial edge of the patella are explored. Since the width of the patellar stop of MPFL was approximately 20 mm, the average distance of its upper edge from the superior pole of the patella was 6.1 mm, which corresponds to the position of the medial superior patellar angle; the average distance of the lower edge from the superior pole of the patella was 23.1 mm, which corresponds to the position of the midpoint of the medial edge of the patella. Most scholars, such as Steensen and Nomura, chose the location of the mid-superior 1/3 of the medial patellar border as the center of the patellar tunnel [13,30,31], and Fithian [32] chose the location of the mid-superior 1/3 of the medial patellar border and the midpoint for MPFL double-beam reconstruction. A small incision is made along the medial edge of the patella at the chosen location, and the medial patellar support band and residual MPFL are incised to reveal the medial edge of the patella, and a 4.5-mm drill is used to create a bone tunnel. The tunnel exit can be located at the lateral edge of the patella (tunnel across the patella) or on the anterior surface of the patella (“L” shaped tunnel, Figure 2). When creating the tunnel, an anterior cruciate ligament guide can be used to place the guide pin and then drill the hole along the guide pin, which can prevent the drill from accidentally entering the joint and damaging the articular cartilage of the patella. If the graft is large, the tunnel can be enlarged appropriately. It is important to note that when using the “L” shaped tunnel, the length of the tunnel should be greater than 2 cm to prevent breakage of the bone bridge of the tunnel.
Figure 3 Anatomic relationship of the MPFL femoral stop with the adductor tuberosity and medial epicondyle of the femur
The patella is then separated medially, between the 1st and 2nd layers. Both the medial patellar support band and the residual MPFL are severed, stopping after cutting the MPFL transverse fibers, so that only the 3rd layer – the joint capsule layer – is intact. The graft can be placed either in layers 1 and 2 or between layers 2 and 3, that is, the graft is in the superficial or deeper layers of the original MPFL. It is recommended to place the graft between layers 2 and 3 for two reasons: first, some fibers of the medial femoral muscle are woven together with the MPFL at a distance of 3 cm from the patellar stop, so if a blunt separation is performed here, it will cause unnecessary damage to the patellar stop of the medial femoral muscle. Second, if the graft is located deep in the MPFL, then it is possible to condition the residual MPFL to be woven with the graft and sutured together before closing the incision. The graft cannot be placed within layer 3 and must be placed outside the joint to avoid graft wear and to allow for healing in the extra-articular environment. Using a long curved forceps, the graft is separated in the selected soft tissue gap all the way to the medial epicondyle of the femur.
The annular end of the graft is fixed to the medial epicondyle of the femur and secured using an absorbable extrusion nail. The graft is then passed between layer 3 (the joint capsule layer) and layer 2 (the original MPFL layer), and the two free ends are locked and braided together with separate sutures.
Two bone tunnels are made in the upper 2/3 of the medial edge of the patella using a 4.5 mm drill bit. Note that the tunnels should be positioned close to the superior pole of the patella to avoid strain on the inferior pole of the patella by the reconstructed ligament and that the tunnel entrances are near the edge of the articular surface. Then, the exit of the tunnel is made on the anterior surface of the patella, where the periosteum has been lifted 8 mm from the medial edge of the patella, and the exit of the patellar tunnel is made here. Note that sometimes the semitendinosus muscle is larger than 4.5 mm in diameter, and if the graft is too thick, the patellar tunnel can be enlarged appropriately. The two free ends of the graft are closed with separate locking sutures that do not exceed the diameter of the original free end. Then, the caudal end of the suture is passed through the patellar tunnel and the graft is tractioned through the patellar tunnel. After final fixation, the overgraft will be cut off.
3.4 Selection of the MPFL femoral stop, assessment of isometricity, and fabrication of the femoral tunnel?
Determining the location of the MPFL femoral stop is the most critical step in MPFL reconstruction surgery (Figure 3). The medial femoral epicondyle and the medial adductor tuberosity are carefully palpated on the medial side of the knee, and a longitudinal incision is made at their anterior margins. If these two anatomic landmarks are not clear to palpation, the knee can be gently flexed, which allows the N cord tendon to be moved back and away from the medial femoral epicondyle to facilitate palpation. If the patient is too fat to palpate clearly, a small incision can be made and a finger can be used to palpate through the incision, or the incision can be extended or changed in direction if needed. After determining the location of the medial epicondyle and adductor tuberosity, a long curved forceps is again used, passing through the patellar incision and through the already separated soft tissue gap, with the tip of the curved forceps reaching the location of the ridge formed by the medial epicondyle and adductor tuberosity. Then, using a 15-gauge blade at the location of the tip of the curved forceps, layers 1 and 2 are incised to reveal the femoral stop of the reconstructed MPFL, which should be located proximal to the medial epicondyle of the femur. A guide pin with an eye is passed through this point and through the femoral epicondyle.
Figure 3 Anatomical relationship of the femoral stop of the MPFL to the medial tuberosity and medial epicondyle of the femur
An Ethibond 5 wire, tied to the guide pin at one end and passing through the patellar tunnel at the other end, was then used as a simulated MPFL and then tied to a length measuring tool such as an Acufex Straining Gauge to measure ACL isometric length, and the knee was moved in full range of flexion and extension to examine the “simulated ligament The change in “simulated ligament” length. Adjust the position of the needle so that the length of the “simulated ligament” changes the least when the knee is flexed: if the “simulated ligament” becomes longer when the knee is flexed, adjust the position of the needle distally, i.e. near the medial epicondyle of the femur; if the knee is straightened “Ellera and Gomes et al [33] suggested that this distance should change by <5 mm, which is considered as the "isometric point".
Once the location of the femoral stop is determined, a bone tunnel is made along the guide pin using a hollow drill to fix the other end of the graft. Typically, the tunnel diameter is no more than 7 mm when using a semitendinosus tendon, but the depth is at least 20 mm; if other grafts are used, the tunnel diameter needs to be adjusted according to the diameter of the graft. If the patient’s bone is lax, a small diameter drill can be used to drill the hole and then expand it to the desired diameter using an expander.
The accuracy of the location of the MPFL femoral stop is critical to the success or failure of the MPFL reconstruction procedure. The original MPFL femoral stop is located on the ridge between the medial epicondyle of the femur and the adductor tuberosity. Several recent articles have discussed the isometric nature of the original MPFL and the changes of the graft in the knee joint after reconstructed MPFL [30]. Normal MPFL tension is greatest in the knee in the extended position and with contraction of the quadriceps. There is no exact definition of the optimal length change of the graft (isometricity), but Ellera et al. suggest that it should be <5 mm [33]. Some surgeons also believe that the requirements for isometric length of the graft are not very strict for MPFL reconstruction surgery. However, intraoperative examination of graft isometricity helps the surgeon to understand the state of the reconstructed graft during knee flexion and extension activities. Therefore, the term "isometric" refers to the ability of the reconstructed MPFL to allow the patella to enter the femoral glide smoothly during early knee flexion and to ensure that the graft does not impact or rub against the femoral condyle. Since the lateral articular surface of the femoral glide is located closer to the end than the medial side, the patella normally contacts the lateral articular surface of the femoral glide first when the knee is flexed.
3.5 Fixation of the graft?
A segment of the graft is first fixed in the tunnel of the femoral stop, which can be fixed with an absorbable extrusion screw. The screws are the same diameter as or 1 mm smaller than the tunnel diameter and are 20 mm long. alternatively, Endopearl can be used to ensure firm lateral femoral fixation. The graft is turned laterally at the tunnel opening and traction is applied through the soft tissue tunnel to the patellar tunnel and through the patellar tunnel, respectively.
When fixing the patellofemoral side, Nomura and Ellera et al. suggest keeping the knee flexed 60º~90º placing the patella in the center of the femoral glide tunnel and maintaining an initial tension of approximately 5 Newtons (0.5 kg) on the graft. After the graft is passed through the patellar tunnel, one suture is closed for temporary fixation. The patella is then checked again for mobility in the flexed 30º or extended position, at which time a very firm end point should be felt; the knee is then flexed and extended, and the range of knee flexion and extension should be unaffected; and, pushing the patella laterally in the flexed 30º position, the patella is displaced in a range of 7 to 9 mm. After confirming proper tension of the graft, the graft is reflexed and sutured to itself (“8” suture, Ethibond nonabsorbable with needle #2 suture) or to soft tissue structures such as the prepatellar periosteum and lateral patellar support band; it can also be secured at the tunnel opening using an Endobutton or button (Figure 4). The method of fixation by suturing the graft to the soft tissue around the bone bridge or bone tunnel can reduce the use of internal fixation materials, but the surgeon needs to consider the patient’s bone condition and the length of the graft to choose the appropriate fixation method.Fithian [25] previously reported a case of a 17-year-old male, weighing 305 pounds (139 kg), 1 year after MPFL reconstruction, who sprained the operated side of the X-rays revealed a fracture of the medial patellar bridge. The authors performed a reoperation to re-fix the graft.
After fixation, the excess tendon was removed and the medial patellar support band and incision were closed. Arthroscopy was used again to examine whether the patellar trajectory had returned to normal during full range of knee flexion and extension. In particular, at the onset of knee flexion, it is important to ensure that the patella can enter the femoral glide smoothly without any impingement or obstruction. Reconstruction of the MPFL results in good patellar stability without patellar hypermobility or further fear of patellar extrapolation, even in severe cases or revisions. Postoperatively, there is no need for drainage placement or cast immobilization, but the knee is protected with a knee brace.
Figure 4 Schematic diagram after MPFL reconstruction
3.6 Use of other grafts?
Noyes and Steensen described the use of the quadriceps tendon as a graft to reconstruct the MPFL. 1/3 of the autologous quadriceps tendon, approximately 10-12 mm wide, is taken. the distal end of the graft is attached to the patella and its free end is turned 90º medially and twisted 180º and then sutured and fixed to the femoral stop.
Steiner described the use of an autologous mid-1/3 quadriceps tendon with patellar bone block for reconstruction of the MPFL. the graft is approximately 1 cm wide and 3-5 mm thick, preserving the deeper layer of the quadriceps tendon and preventing postoperative scarring of the suprapatellar capsule. The distal end of the graft was attached to the patellar bone block, which was 1 cm2×5 mm (thick) in size and cut with a swing saw. The free end of the tendon was similarly sutured using Ethibond 2 gauge locking edge. At the location of the MPFL patellar stop, two bone tunnels are made side by side using a 4.5mm diameter hollow drill, so that the two bone tunnels are connected to form a 9mm x 4.5mm bone tunnel. at the location of the MPFL femoral stop, a 1 x 1cm2 bone groove is dug with a bone knife, centered on the guide pin, at a depth just deep enough to embed the graft bone block. The femoral side was fixed with 4.0 mm cancellous tension screws, and the patellar side was fixed with sutures, or with buttons.
The difference for the use of artificial ligaments as grafts is that the location of the MPFL femoral stop can be fixed using a double portal nail fixation technique. After confirming the femoral stop, a small piece of periosteum (approximately 1 cm x 2-3 cm in size) is lifted from this area, centered on the guide pin, to expose the subperiosteal cortical bone. The ligament is fixed with the first portal nail in a posterior position, then the ligament is reflexed forward and overlapped with itself, and then fixed with the second portal nail. The two portal nails and the artificial ligament should be covered with lifted periosteum as much as possible to promote early healing of the portal nail area. In addition, the artificial ligament should be covered by the incised medial patellar support band as much as possible.
4.Postoperative management and rehabilitation planning for MPFL reconstruction surgery?
Although there are many surgical methods for reconstructing MPFL, the principles and surgical techniques are basically similar and also conform to the general rules of ligament reconstruction. Therefore, the postoperative rehabilitation plan is similar when comparing different reconstruction methods.
Most articles agree that after MPFL reconstruction, patients need to wear a brace for protection (usually without plaster immobilization). Most agree that the brace should be worn for 6 weeks, whereas Noyes et al. used a quadriceps tendon to reconstruct the MPFL and concluded that 3 weeks of postoperative brace protection was sufficient. The brace should be fixed in the extension position, and some use a hinged brace set at an initial angle of full extension to 30º. Flexion exercises can be started on postoperative day 2 to 3, using CPM or with the assistance of a rehabilitation therapist. Knee flexion to 90º is usually achieved within 3 to 4 weeks postoperatively (Nomura et al. used artificial ligaments to reconstruct the MPFL and concluded that postoperative knee flexion exercises using CPM with a starting angle setting of 0º to 40º can be increased by 10º per day, and knee flexion of 90º is usually achieved by 7 days postoperatively). If the patient is still unable to flex the knee to 90º at 4-6 weeks postoperatively, physical therapy must be intensified; if knee stiffness occurs that cannot be resolved by physical therapy, pushing under anesthesia or further treatment can be performed at 9-12 weeks postoperatively; Noyes et al. concluded that if the knee flexion angle does not reach 90º at 3 weeks postoperatively, pushing under anesthesia can be performed. Exercises for quadriceps isometric contraction, straight leg raising, mild pushing of the patella, and mild active knee flexion were started on postoperative day 2. On the 2nd to 3rd postoperative day, the patient can perform partial weight-bearing with the aid of a double crutch, as much as the patient can tolerate, but not more than 50% of the body weight (generally about 25% of the body weight). Patients must wear a brace when performing weight-bearing or walking exercises. Full weight-bearing is usually performed 4 weeks after surgery. Two weeks after surgery (after stitch removal), patients are allowed to remove the brace when bathing or moving around the room. However, for 6 weeks postoperatively, patients are required to wear the brace while walking and sleeping. After 3 months postoperatively, patients were allowed to begin jogging and light physical activity. When resuming physical activity, patients can wear a simple knee brace and patella stabilization brace for protection. If the patient’s knee flexion and extension range of motion and quadriceps muscle strength return to normal, full physical activity can begin, which generally takes 6 months.
5. Summary
In the 1990s, the importance of MPFL gradually began to be recognized. Recently, biomechanical studies have shown that the MPFL is the predominant patellofemoral stabilizing structure in the medial knee. Acute patellar dislocation causes MPFL fracture and, moreover, all patients with recurrent patellar dislocation have MPFL abnormalities or MPFL deficiency. Therefore, MPFL deficiency is the main cause of recurrent patellar instability after acute patellar dislocation, and, in patients with recurrent patellar dislocation, MPFL fracture is the main causative factor in addition to the known predisposing factors. Based on the results of clinical studies and biomechanical tests on MPFL injuries, some physicians have recently started to perform one-stage MPFL repair for acute patellar dislocations, but the long-term follow-up results are still unknown.
Since 1992, results of MPFL reconstruction have been gradually reported.Galeazzi used semitendinosus tendon to reconstruct the MPFL by tendon fixation.The first use of artificial ligaments was by Lemaire, who used them to strengthen the medial patellar support band in 1986 with good results.In 1992, Ellera Gomes introduced the use of artificial ligaments method for the reconstruction of the MPFL. Moreover, he also proposed the use of a measurement tool to find the optimal fixation point on the femoral side of the MPFL. He concluded that a change of <5 mm in the distance between the MPFL patellar fixation point and the medial femoral epicondyle fixation point during knee flexion and extension is the location of the optimal femoral fixation point.
The following issues need to be noted for MPFL reconstruction surgery.
1. regarding the angle of knee flexion during ligament fixation, Ellera Gomes [33] suggested a position of 90º of knee flexion. nomura et al. suggested that the maximum distance between the MPFL patellar stop and femoral stop is at 0º~60º of knee flexion, and in the 60º position of knee flexion, the operator can easily check whether the patella is in a normal position (the center of the femoral glide groove), so the authors recommend a flexed knee 60º fixation ligament.
2. Regarding the initial tension of the ligament during reconstruction of the MPFL, it is hoped that the reconstructed ligament will maintain sufficient tension so that it is neither too tight nor too loose during the full range of knee flexion and extension. Nomura used a spacer (6 mm in height) between the graft and the femoral epicondyle when fixing the graft and maintained a tension of 0.5 kg in the ligament. No other study results are available.
3. Regarding the graft fixation method, many scholars use suture fixation to fix the tendon to the bone or medial femoral muscle, and the knee joint is not braked after surgery. Therefore, if the patient is weight-bearing without postoperative support, the strength of the suture fixation is not sufficient to withstand the external force, and laxity may occur. Therefore, the fixation method should be determined according to the specific surgical procedure, and the knee joint should be protected by a knee brace after surgery, and the full weight-bearing time should be 4 weeks after surgery to ensure the full healing of the transplanted ligaments.
4. Although there are many predisposing factors for lateral patellar dislocation, the vast majority of patients develop MPFL rupture after the first patellar dislocation, and patients with recurrent patellar dislocation have MPFL rupture/loss of function. Therefore, it can be assumed that the MPFL is the most basic limiting structure and should be reconstructed first. However, in severe cases, such as the presence of a high patella (ratio more than 1.3) and a Q angle of more than 25º, reconstruction of the MPFL alone may not completely solve the problem. In patients with high patella, due to anatomical abnormalities, isometric reconstruction may not be obtained if MPFL is reconstructed, so we do not recommend simple MPFL reconstruction for them, and in patients with severe force line abnormalities and Q-angle exceeding 25º, simple MPFL reconstruction surgery is also not applicable.
In conclusion, the advantages of MPFL reconstructive surgery are (1) anatomical reconstruction of the ligament; (2) it is applicable to many types of patellar dislocation, and, it can be combined with other procedures simultaneously to treat severe patellar dislocation; and (3) it has minimal impact on the knee extension device.
Many MPFL reconstruction procedures have been performed, and the results of these procedures have shown that for the treatment of recurrent patellar dislocations, MPFL reconstruction is superior to previous surgical methods.