Department of Orthopaedic Surgery, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, USA.
Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, USA.
Am J Sports Med. 2023 Jun;51(7):1765-1776. doi: 10.1177/03635465231165296. Epub 2023 Apr 24.
Medial patellofemoral complex (MPFC) reconstruction plays an important role in the surgical treatment of patellar instability. Anatomic reconstruction is critical in re-creating the native function of the ligament, which includes minimizing length changes that occur in early flexion. Anatomic risk factors for patellar instability such as trochlear dysplasia, patella alta, and increased tibial tuberosity to trochlear groove (TT-TG) distance have been shown to influence the function of the MPFC graft in cadaveric studies, but the native length change patterns of the MPFC fibers in knees with anatomic risk factors have not been described.
To describe the in vivo length changes of the MPFC fibers in knees with anatomic risk factors for patellar instability and identify the optimal attachment sites for MPFC reconstruction.
Controlled laboratory study.
Dynamic computed tomography imaging was performed on the asymptomatic knee in patients with contralateral patellar instability. Three-dimensional digital knee models were created to assess knees between 0° and 50° of flexion in 10° increments. MPFC fiber lengths were calculated at each flexion angle between known anatomic attachment points on the extensor mechanism (quadriceps tendon, MPFC midpoint [M], and patella) and femur (1, 2, and 3, representing the proximal to distal femoral footprint). Changes in MPFC fiber length were compared for each condition and assessed for their relationships to morphologic risk factors (trochlear depth, Caton Deschamps Index [CDI], and TT-TG distance).
In 22 knees, native MPFC fibers were found to be longer at 0° than at 20° to 50° of flexion. Length changes observed between 0° and 50° increased with the number of risk factors present. In the central fibers of the MPFC (M-2), 1.7% ± 3.1% length change was noted in knees with no anatomic risk factors, which increased to 5.6% ± 4.6%, 17.0% ± 6.4%, and 26.7% ± 6.8% in the setting of 1, 2, and 3 risk factors, respectively. Nonanatomic patella-based attachments were more likely to demonstrate unfavorable length change patterns, in which length was greater at 50° than 0°. In patellar attachments, an independent relationship was found between increasing length changes and TT-TG distance, while in quadriceps tendon attachments, a trend toward a negative relationship between length changes and CDI was noted. All configurations demonstrated a strong relationship between percentage change in length and number of morphologic risk factors present, with the greatest influence found in patella-based attachments.
The MPFC fibers demonstrated increased length changes in knees when a greater number of morphological risk factors for patellar instability were present, which worsened in the setting of nonanatomic configurations. This suggests that the function of the intact MPFC in patients with anatomic risk factors may not reflect previously described findings in anatomically normal knees. Further studies are needed to understand the pathoanatomy related to these changes, as well as the implications for graft placement and assessment of length changes during MPFC reconstruction techniques.
MPFC length change patterns vary based on the number of morphologic risk factors for patellar instability present and should be considered during reconstructive procedures.
内侧髌股韧带复合体(MPFC)重建在髌股不稳的手术治疗中起着重要作用。解剖重建对于重建韧带的固有功能至关重要,这包括最小化早期弯曲时发生的长度变化。解剖学上的髌股不稳风险因素,如滑车发育不良、高位髌骨和增加的胫骨结节到滑车沟(TT-TG)距离,已在尸体研究中表明会影响 MPFC 移植物的功能,但尚未描述具有解剖学风险因素的膝关节中 MPFC 纤维的固有长度变化模式。
描述具有髌股不稳解剖学风险因素的膝关节中 MPFC 纤维的体内长度变化,并确定 MPFC 重建的最佳附着点。
对照性实验室研究。
对患有对侧髌股不稳的患者进行无症状膝关节的动态计算机断层扫描成像。创建三维数字膝关节模型,以评估 0°至 50°之间每 10°递增的膝关节。在每个屈曲角度下,通过已知的伸肌(股四头肌肌腱、MPFC 中点[M]和髌骨)和股骨(1、2 和 3,代表股骨近端到远端足迹)之间的解剖附着点计算 MPFC 纤维的长度。比较了每种情况下 MPFC 纤维长度的变化,并评估了它们与形态学风险因素(滑车深度、Caton-Deschamps 指数[CDI]和 TT-TG 距离)之间的关系。
在 22 个膝关节中,发现固有 MPFC 纤维在 0°时比在 20°至 50°时更长。在 0°至 50°之间观察到的长度变化随着存在的风险因素数量而增加。在 MPFC 的中央纤维(M-2)中,在没有解剖学风险因素的膝关节中,观察到 1.7%±3.1%的长度变化,而在存在 1、2 和 3 个风险因素的情况下,分别增加至 5.6%±4.6%、17.0%±6.4%和 26.7%±6.8%。非解剖学的基于髌骨的附着更可能表现出不利的长度变化模式,其中 50°的长度大于 0°。在髌骨附着处,发现长度变化与 TT-TG 距离之间存在独立的关系,而在股四头肌肌腱附着处,发现长度变化与 CDI 之间存在负相关的趋势。所有配置均表现出长度变化百分比与存在的形态学风险因素数量之间的强烈关系,在基于髌骨的附着处发现最大的影响。
当存在更多的髌股不稳形态学风险因素时,膝关节中的 MPFC 纤维表现出更大的长度变化,在非解剖学配置下,这种变化会恶化。这表明,具有解剖学风险因素的患者中完整的 MPFC 的功能可能无法反映先前在解剖学正常的膝关节中描述的发现。需要进一步研究以了解与这些变化相关的病理解剖学,以及在 MPFC 重建技术中移植物放置和长度变化评估的意义。
MPFC 长度变化模式取决于髌股不稳的形态学风险因素的数量,在进行重建手术时应予以考虑。