Diseño instruccional en la formación continuada

Many types of tears occur in the meniscus. Major tear types are shown in Figure 2.2. Tear position is classified by dividing the meniscus into 3 circumferential segments (anterior, mid- dle, posterior) and 4 radial segments (meniscosynovial junction, outer third, middle third, inner third) (Cooper et al. 1990). Different tear phenotypes (combinations of tear type, tear position, and which meniscus is torn) are associated with different etiologies. Broadly speaking, menis- cus tear etiology falls into two groups: (1) acute tears, which are associated with a specific overload event/injury and are common in younger people and (2) degenerative tears, which are not associated with a specific injury.

Meniscus injury and meniscus-related surgeries are very common. Arthroscopic treatment of meniscus injuries comprised 10–20% of all surgeries in the U.S. in 1990 (Greis et al. 2002). Meniscus tears are associated with three causes in roughly equal proportion: (non-professional) sports-related injury, injuries unrelated to sports, and no identifiable cause (Drosos and Pozo 2004). A third of non-sporting injuries are sustained rising from or descending to a squatting position. In young people, meniscal injury is accompanied by a snapping or popping sensation (Wagemakers et al. 2008). Horizontal cleavage, flap, and complex tears are considered degen- erative because they are more common in older patients (age > 40 years) who cannot recall a specific injury event (Drosos and Pozo 2004). Simple longitudinal tears and bucket handle

tears (which may have the “handle” torn into two pieces) are considered acute/traumatic. Lon- gitudinal tears and bucket-handle tears typically occur in people aged 20–30 year in the middle and posterior sections of the meniscus (Lento and Akuthota 2000; Oberlander and Pryde 1994; Hardin et al. 1992). Shear stress has been hypothesized to be important in the formation of vertical and horizontal tears (Smillie 1978). The prevalence of meniscal tears increases with age, from ~25% per knee at age 50–59 years to ~45% at age 70–90 years (Englund et al. 2008). Drosos and Pozo (2004) have proposed that degenerative changes prior to 20 years of age di- minish the elasticity of the meniscus and increase its susceptibility to injury.

The medial meniscus is more vulnerable to injury than the lateral meniscus because it is attached to the medial collateral ligament and so has less mobility (Lento and Akuthota 2000). Medial meniscus tears are 2–5 times as common as lateral meniscus tears (Campbell et al. 2001; Englund et al. 2008; Burk et al. 1988). The prevalence of lateral meniscus tears increases for sport-related meniscus tears, but is still less than the prevalence of medial meniscus tears (Drosos and Pozo 2004). In the sagittal plane, the medial tibial plateau is concave up (McDer- mott 2006). This could promote crushing and tearing of the medial meniscus.

Meniscus tears are considered to be a cause of osteoarthritis (Cohen et al. 2007; Englund et al. 2008). In individuals with risk factors for osteoarthritis (age 45–55 years), 64% had menis- cus lesions and 79% had cartilage lesions (Laberge et al. 2012). Meniscus tears (as identified in 1.5T MRI) are much more common in people with radiographic evidence of osteoarthritis (an osteophyte or worse) than in those without (60% vs. 25%) (Englund et al. 2008). In patients with advanced knee osteoarthritis, the most common type of meniscal abnormality was a hy-

pertrophied displaced tear (Jung et al. 2010). Meniscus injury is a risk factor for developing osteoarthritis after ACL injury (Øiestad et al. 2009). At least part of the correlation between meniscus tears and osteoarthritis is probably mediated by tears being treated by meniscectomy, with meniscectomy being the proximal cause of ensuing osteoarthritis.

Meniscus tears can also adversely affect knee structures other than the articular cartilage, such as the ACL (Arnold et al. 1979). Conversely, injuries to the ACL make meniscus injury more likely (Bellabarba et al. 1997). In ACL-deficient knees, the medial meniscus load in- creases by 50–200%, depending on knee flexion (Allen et al. 2000; Papageorgiou et al. 2001). More than one third of meniscus tears are associated with an ACL injury (Poehling et al. 1990), and about one third of knees with ACL injury also have meniscus tears, mostly of the medial meniscus (Warren and Marshall 1978). Patients with ACL tears due to a jumping injury are more likely to have meniscus tears than patients with a non-jumping injury (Paul et al. 2003).

Optimal management of meniscus tears is uncertain. Surgeons tend to consistently agree on the treatment of meniscus tears (Dunn et al. 2004). However, it is still difficult to definitively say whether any given tear can be left untreated (Duchman et al. 2015). There is concern about tear-induced joint instability or post-surgical rehabilitation causing tear extension (Lento and Akuthota 2000). At least some incomplete tears appear to be stable and best left untreated. Longitudinal partial-thickness tears, stable (< 5 mm long) full-thickness peripheral tears, and short (< 5 mm long) radial tears may not require surgical repair (Lento and Akuthota 2000). Calling a tear stable means that the tear doesn’t affect the local rigidity of the meniscus upon (arthroscopic) manipulation. Definitions do vary; Duchman et al. (2015) define a stable tear

as one that cannot be moved into the intercondylar notch, and say there is little consistency in definitions between studies. Treatment for incomplete longitudinal tears and complete sta- ble longitudinal tears is considered to not be required (Feucht et al. 2015; Pujol and Beaufils 2009; Fitzgibbons and Shelbourne 1995) . Root tears, complete radial tears, and bucket handle tears, however, are mechanically relevant and should be repaired as soon as feasible (Feucht et al. 2015; LaPrade et al. 2014; Forkel et al. 2014; Ode et al. 2012; Schillhammer et al. 2012; Kluczynski et al. 2013). A rule of thumb is that any medial meniscus vertical lesion ≥ 10 mm long that is associated with ACL tear requires repair (Seil et al. 2009). These judgment calls are not especially accurate. Considering specifically tears discovered during ACL repair, 4–22% of untreated lateral meniscus tears undergo subsequent reoperation in a 6-year followup, as do 10–66% of untreated medial tears (Duchman et al. 2015; Pujol and Beaufils 2009). Lateral meniscus tears tend to scar and heal better than medial meniscus tears if left in situ (Seil et al. 2009). Medial meniscus tears tend to produce secondary tears if left in situ. Overall, the behav- ior of tears is not predictable at this time, and judgment calls are made based on accumulated experience rather than mechanical or biological rationale.